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ELECTROLYSIS IN CONCRETE 












/ 


I 

DEPARTMENT OF COMMERCE 


Technologic Papers 

of THE 

Bureau of Standards 

S. W. STRATTON, Director 3C 

. — H t» 

No. 18 

ELECTROLYSIS IN CONCRETE 


BY 

E. B. ROSA, Chief Physicist 

BURTON McCOLLUM, Associate Physicist, and 

0. S. PETERS, Assistant Physicist 

Bureau of Standards 


[MARCH 19* 1913] 



WASHINGTON 

GOVERNMENT PRINTING OFFICE 
1913 *1 i 4- ; 






Monograph 







ADDITIONAL COPIES 

OF THIS PUBLICATION MAY BE PROCURED FROM 
THE SUPERINTENDENT OF DOCUMENTS 
GOVERNMENT PRINTING OFFICE 
WASHINGTON, D. C. 

AT 

35 CENTS PER COPY 



0. OF 9, 
may 15 1915 



CONTENTS 


V, 




Page 


I. Introduction. 5 

II. Investigations relating to the nature and cause of the phe¬ 
nomena RESULTING FROM THE PASSAGE OF ELECTRIC CURRENTS 
THROUGH CONCRETE. 9 

1. Form and composition of test specimens.. 9 

2. Electrical circuits. 10 

3. Arrangement of specimens in vessels. 11 

4. Electrolyte. 12 

5. Miscellaneous conditions of tests. 12 

6. Anode tests on high voltage. 13 

7. Anode tests on low voltage... 16 

8. Tests on materials other than iron as anode. 19 

(а) Copper, brass, carbon, and copper-clad steel. 19 

(б) Tests on aluminum anodes. 22 

9. Cathode effects using iron, brass, copper, carbon, and aluminum 

electrodes. 24 

10. Bond tests of cathode specimens. 28 

11. Cause of softening action at cathode. 30 

12. Effect of electric currents on the mechanical strength of nonrein- 

forced concrete. 40 

13. Cause of cracking of reinforced concrete by electric currents. 44 

(a) Experiments with specimens containing loose electrodes. 46 

( b ) Experiments with carbon electrodes. 46 

(c) Experiments with collapsible electrodes. 47 

(d) Measurement of force produced by corrosion of iron in 

concrete. 49 

14. Rise of electrical resistance of reinforced concrete due to flow of 

current... 55 

(а) Rise of resistance of anode specimens. 55 

(б) Determination of the location of the rise of resistance.... 56 

(c) Cause of rise of resistance. 60 

( d ) Rise of resistance of cathode specimens. 61 

( e ) Effect of the addition of salts on the resistance of concrete. 64 

(/) Rise of resistance of concrete buried in damp earth. 66 

(g) Rise of resistance of concrete setting in air. 67 

15. Variations in the magnitude of electrolytic corrosion of iron in 

concrete. 71 

(a) Corrosion tests using different cements. 73 

( b ) Effect of temperature on efficiency of corrosion. 76 

(c) Corrosion of iron in concrete containing foreign ingredi¬ 

ents. 84 

(< d ) Effect of waterproofing compounds. 85 

(e) Effect of salt and calcium chloride. 88 

✓ 


3 


































4 Technologic Papers of the Bureau of Standards 

II. Investigations relating to the nature and cause of the phe¬ 
nomena RESULTING FROM THE PASSAGE OF ELECTRIC CURRENTS 
Through concrete —Continued ’ Page 

16. Electrolytic cleaning of rusted iron. 89 

17. Laboratory experiments with proposed methods for minimizing 

electrolysis in reinforced concrete. 92 

(a) Reducing the efficiency of corrosion by chemical means.. 92 

(b ) Painting or coating the iron before embedding it in the 

concrete. 96 

(c) Specific resistance of concrete, tests of waterproofing in¬ 

tegrals, and resistance measurements of granite and 
limestone. 97 

(d) Tests on waterproofing paints and membranes for con¬ 

crete. 106 

III. Possibilities of trouble from electrolysis in concrete structures 

UNDER PRACTICAL CONDITIONS. 113 

18. Conditions necessary for damage to occur. 113 

19. Sources of stray currents. 115 

20. Increased damage due to presence of salt. 117 

21. Some specific cases of trouble. 118 

22. Procedure in making voltage measurements on concrete struc¬ 

tures. 122 

IV. Protective measures. 123 

23. Exclusion of salt. 123 

24. Waterproofing below grade. 123 

25. Addition of waterproofing compounds. 124 

26. Construction of foundations. 124 

27. Electric wiring. 125 

28. Insulation of pipes and cables. 125 

29. Making the reinforcing material negative. 126 

30. Improving the negative return of railways. 127 

31. Grounding of metallic conduits.. 127 

V. Conclusions. 131 

Appendix—Bibliography. 137 

























ELECTROLYSIS IN CONCRETE 


By E. B. Rosa, Burton McCollum, and O. S. Peters 


I. INTRODUCTION 

During the last few years attention has been called to the pos¬ 
sibility of damage to reinforced-concrete structures by stray 
currents from electric railways and other power sources. The 
laboratory experiments of Toch, 1 Knudson, 2 and hangsdorf 3 in 
1906 and 1907 showed clearly that under certain circumstances 
the passage of electric currents from the reinforcing material into 
the concrete gave rise not only to serious corrosion of the reinforc¬ 
ing material, but also to cracking and splitting of the surrounding 
concrete. Since then numerous laboratory experiments have been 
carried out by various investigators, all tending to confirm the 
earlier observations in regard to the cracking of the concrete, but 
giving rise to various conflicting theories as to the cause of the 
phenomena observed. Following the early demonstrations of the 
possibility of damage to concrete by electric currents, reports of 
serious damage to certain concrete buildings and bridges became 
current and considerable apprehension has been hroused in some 
quarters that great damage may be in progress due to this cause. 
The subject was brought directly before the Bureau of Standards 
by letters of inquiry from engineers, contractors, and corporations 
requesting information in regard to the probable extent of the 
damage and the most practicable methods of preventing it. 

1 Max. Toch: The Electrolytic Corrosion of Structural Steel, J. Am. Electro-Chem. Soc., 9, p. 77; 1906. 

2 A. A. Knudson: Electrolytic Corrosion of Iron and Steel in Concrete, Trans. A. I. E. E., 26, p. 231; 1907. 

8 A. S. Eangsdorf: Electrolysis in Reinforced Concrete, J. Assn, of Eng. Soc., 42, p. 69; 1909 - 


5 





6 Technologic Papers of the Bureau oj Standards 

Although a good deal of work had been done showing that under 
certain conditions, readily producible in the laboratory, blocks of 
reinforced concrete could be split and broken up by electric cur¬ 
rents, there remained a wide diversity of opinion as to the cause 
of the observed phenomena. Nothing had been published show¬ 
ing to what extent and under what circumstances damage might 
be expected under practical conditions, or how trouble from this 
source might best be prevented. Recognizing the great practical 
importance of the subject the Bureau of Standards has undertaken 
a thorough investigation into the nature and cause of the phenom¬ 
ena observed in concrete under the influence of electric currents, 
the extent to which damage has occurred or is likely to occur in 
practice from this cause, and the best methods of mitigating the 
trouble under practical conditions. The work was begun during 
the summer of 1910 and certain phases of the investigation are 
still in progress, but enough work has been completed to justify 
the publication of a report of progress at this time. 

At the time the present work was undertaken the following 
facts had seemingly been established by the work of other inves¬ 
tigators : 

1. That, as far as the experiments went, the passage of an 
electric current of whatever magnitude from embedded iron to 
concrete in the presence of moisture resulted in cracking of the 
concrete and rusting of the embedded iron. These cracks ex¬ 
tended radially from the iron and opened out gradually as the 
test progressed until the block in which the iron was placed 
would go to pieces or could be easily broken. 

2. The passage of an electric current from concrete to embedded 
iron resulted in no damage whatever to the block, except in one 
or two extreme cases, where the voltage used was very high. 
This led to the conclusion that no damage is to be expected 
where current is found flowing from concrete to iron—that is, 
where the iron is cathode. 

3. The specimens of concrete showed a tendency to protect the 
iron contained in them by virtue of a large increase of resistance 
as the test proceeded. This increase is not entirely permanent, 


7 


Electrolysis in Concrete 

as is evidenced by measurements taken before shutting off the 
current and again some time after stopping the current and is 
found in greatest degree where embedded iron is anode—that is, 
where the current passes from iron to concrete. Where the iron 
is cathode, the rise of resistance occurs, but is not nearly so great. 
There is, however, no instance in any previous investigation of 
this increase of resistance being sufficient to reduce the current 
to a negligible value. 

4. The voltage apparently had nothing to do with the phe¬ 
nomena observed beyond affecting the magnitude of the current 
and consequently the rapidity of the action. 

Beyond these four points there appeared to be little agree¬ 
ment among the various investigators. Especially contradictory 
were the theories advanced to explain the phenomena observed. 
As the result of experimental evidence of record, at least five 
different theories had been advanced to account for the destruc¬ 
tion of the concrete. These were: (1) Gas pressure . 4 When an 
electric current passes between electrodes in an electrolyte, more 
or less gas is evolved at the electrodes, and it was held that this 
gas, liberated within the mass of the concrete, escaped with such 
difficulty that sufficient pressure was developed to crack the con¬ 
crete. (2) Heating . 5 The passage of an electric current through 
concrete generates heat therein, and if the current density is high 
the concrete may become quite hot. It was shown that local 
heating by a flame or other means would produce cracking, and 
the conclusion was therefore drawn that the cracking of the con¬ 
crete under the influence of the electric current was due to its 
heating effect. (3) Electrochemical deterioration of the concrete. 
The early observations of Toch, Langsdorf, and others led them 
to believe that the concrete underwent a marked chemical or 
physical change, whereby it became soft and fragile and that this 
apparent decay of the concrete was in large measure responsible 
for the cracking observed. (4) Mechanical pressure. When a 
current passes from iron into the concrete, corrosion of the iron 
results with the ultimate production of insoluble compounds of 


« A. J. Nicholas: Tests on Effect of Electrolysis in Concrete, Eng. News, 60, p. 710. 
6 O. E. Eltinge: Tests on Effect of Electrolysis in Concrete, Eng. News, 63, p. 373. 



8 Technologic Papers of the Bureau of Standards 

iron, largely the oxides. These form near the surface of the iron 
and occupy about 2.2 times as much space as the original iron 
from which they were formed. It is evident, therefore, that con¬ 
siderable mechanical pressure might be developed in this way 
between the surface of the iron and the concrete, possibly suffi¬ 
cient to produce the cracking observed. This theory had per¬ 
haps been most widely accepted, but it was directly opposed by 
Upson and Barker 6 as a result of their experiments with collap¬ 
sible electrodes. These experimenters used hollow electrodes 
made by rolling thin sheet iron into cylindrical forms, the idea 
being that they would collapse readily, and thus relieve any radial 
pressure that might be developed at the surface of the electrode. 
When these electrodes were used, the concrete was found to crack 
in very much the same manner as when solid electrodes were 
employed, and it was therefore concluded that there was no 
appreciable pressure developed on the surface of the electrode. 
Upson and Barker advanced the theory that the cracking was 
due to the formation of deposits of iron compounds , chiefly hydrates, 
within the pores of the concrete , and these on oxidation developed 
the forces which are responsible for the cracking of the concrete. 
These various theories will be discussed in detail hereafter in 
connection with the description of the experimental work carried 
out at the Bureau of Standards. 

In addition to the laboratory investigations discussed above, a 
number of cases had been reported in the technical press in which 
damage of a serious nature had occurred to certain concrete 
buildings, bridges, and other structures in which the damage was 
attributed to stray currents from power circuits. Whether or not 
the problem was as serious from a practical viewpoint as these 
reports led many to believe, the possibility of trouble having been 
established, a thorough investigation of the subject became 
imperative. Such an investigation was authorized by act of 
Congress June 17, 1910, and a special appropriation made for 
carrying on the work. 

6 Barker and Upson: Experimental Studies of the Electrolytic Destruction of Reinforced Concrete, Eng. 
News, 66, p. xo. 



Electrolysis in Concrete 


9 

As mentioned above the investigation has consisted of three 
parts, as follows: 

I. Laboratory investigations relating to the nature and cause 
of the phenomena produced by the passage of electric currents 
through concrete. 

II. Investigations in the field with the view of establishing 
the probable extent of the danger in practice and the circum¬ 
stances under which trouble is most likely to occur. 

III. A study of the various possible means of mitigating 
trouble from this source, leading to specific recommendations. 

II. INVESTIGATIONS RELATING TO THE NATURE AND 

CAUSE OF THE PHENOMENA RESULTING FROM THE 

PASSAGE OF ELECTRIC CURRENTS THROUGH CON¬ 
CRETE 

1. FORM AND COMPOSITION OF TEST SPECIMENS 

At the outset of the investigation a number of the experiments 
described by previous experimenters were repeated in order to 
verify their results and also to afford an opportunity for studying 
at first hand the phenomena previously observed. At the same 
time numerous modifications of these experiments, as well as many 
radically different ones, designed to throw light on particular 
phases of the subject, were instituted. In this preliminary work 
one general type of specimen was adhered to as far as practicable. 
A number of well-known brands of Portland cement, all of which 
conform to the requirements of the standard specifications for 
Portland cement, were selected, together with sand and stone 
similar to those used in large quantities by builders in the city of 
Washington for reinforced concrete construction work. Using 
filtered Potomac River water, these ingredients were made into a 
i: 2j^2:4 concrete, proportions which gave a fairly dense aggregate. 
In many experiments, especially where chemical analyses were 
to be made, quartz sand and distilled water were used, as noted 
later. The specimens were molded into cylinders 6 inches in diam- 


io Technologic Papers of the Bureau of Standards 

eter and 8 inches long, with an electrode embedded in the axis of 
each cylinder, as shown in Fig. i. 

The specimens were allowed to remain in the molds until 
set sufficiently for handling and then removed and buried in wet 
sand for approximately 20 days. At the end of this time they 
were taken out of the sand and placed in an inclosed case, where 
they were wet down occasionally until used. 

Where iron served as material for the embedded electrode it 
was cleaned of scale and rust by pickling in dilute sulphuric 
acid. After the pickling process was completed the iron was 
removed from the acid, dipped in lime water and immediately 
embedded in the specimen, after being numbered and weighed. 



This insured the entire absence of rust to begin with. Electrodes 
other than iron were sandpapered or otherwise cleaned to a bright 
surface before embedding. In the report of each experiment the 
type of electrode used is given as well as any departure from the 
procedure described above. 

2. ELECTRICAL CIRCUITS 

Direct electric current for the experiments was obtained from 
two sources. One of these was the 115-volt power circuit of the 
bureau and the other the 15-volt circuit of a small motor-generator 
set. The wires from these circuits were led into cases containing 






























II 


Electrolysis in Concrete 

the specimens under test and terminated in binding posts at 
convenient points. Intermediate voltages were obtained by 
connecting a small storage battery in the circuit of the 15-volt 
generator and tapping it at suitable points, or by connecting a 
metallic resistance across the 15-volt or 115-volt circuit, as the 
case demanded, and shunting a certain portion of it with the 
specimen. The currents used by the specimens were all very 
small. Still another way of getting intermediate and equal 
voltages on specimens was to connect two specimens in series, 
and, in parallel with the one having the highest resistance, place a 
water rheostat. These water rheostats were made by filling a 



glass jar with distilled water and placing two movable sheet-iron 
electrodes in the jar. The resistance of these rheostats could be 
varied from 200 to 5000 ohms and they served the purpose very 
satisfactorily. 

3. ARRANGEMENT OF SPECIMENS IN VESSELS 

Each specimen under test was placed in an earthenware jar 8% 
inches in diameter and 9 inches deep. For an outer electrode an 
8 by 24 inch piece of No. 24 gauge sheet-iron was rolled into a 
cylinder 7 inches in diameter by 8 inches long and placed around 
the specimen. The arrangement is shown in Fig. 2. The jar, 





































12 Technologic Papers of the Bureau of Standards 

with the exception of cases otherwise designated, was filled to 
about i inch from the top of the specimen with tap water. 
Rubber-covered wire leads were soldered to the outer sheet-iron 
electrode and to the projecting end of the embedded metal. By 
connecting these wires to the proper poles of the electric circuits 
the embedded metal could be made either anode or cathode. 
The jars were set on shelves in a case'provided with glass doors. 
The shelves were fitted with drip pans connected to a common 
drain pipe. Two cases had spaces for 180 jars. 

4. ELECTROLYTE 

The term “tap water” as here used means Potomac River 
water after being filtered for domestic use in the city of Wash¬ 
ington. The use of this water for electrolyte in all but a few 
cases was justified by a chemical analysis which shows that its 
principal foreign ingredient is lime, which is present only to the 
extent of a few parts in a million. The water evaporated from 
each jar at an approximate rate of ioo cc per week. A test 
extending over a period of 50 weeks would, consequently, permit 
a total evaporation of water about twice during that time, since 
the jar contained nearly 3000 cc of liquid when the specimen was 
immersed. The concentration of the impurities in the water 
used would therefore be very low in the electrolyte at the end 
of the test. 

In none of the tests recorded in the section on anode effects or 
in the section dealing with cathode effects, was a complete change 
of electrolyte made. As the water evaporated the jars were 
refilled to the proper amount; the electrolyte retained, in addi¬ 
tion to the impurities of the water, the compounds diffused from 
the immersed specimen and those absorbed from the atmosphere 
above it. 

5. MISCELLANEOUS CONDITIONS OF TESTS 

The description of the phenomena observed is given under two 
heads, viz, (1) anode effects, or those effects observed where the 
current flows from the embedded iron into the concrete, and (2) 
cathode effects, or those occurring when the current flows from the 


Electrolysis in Concrete 


13 


concrete to the embedded iron. In each case experiments were 
carried out both under high and low voltage, and as the results 
were radically different in the two cases, they are discussed below 
under separate heads. In the high-voltage tests the specimens 
were subjected to voltages varying from about 50 to 70 volts, 
and the current flow was continuous, except for infrequent and 
irregular intervals when work was being done on the specimens 
under test or on the electric circuits to which they were connected. 
The time during which they were disconnected amounted to less 
than 1 per cent of the total time. In the low-voltage tests the 
current was maintained for 7^ hours each working day for the 
first 8 weeks, after which the current was on for 24 hours each 
day, with the exception of Sundays and holidays and an occasional 
short interval when the machine was shut down for repairs. In 
calculating the number of hours of a test only the time during 
which current flowed was considered. 

6. ANODE TESTS ON HIGH VOLTAGE 

Only a comparatively small number of specimens were tested on 
high voltage, because such conditions are abnormal and would 
rarely, if ever, be encountered in practice. A few of these were 
made, however, to check the observations of previous experi¬ 
menters, and the results noted in these tests are recorded briefly 
below. In the preliminary tests on high voltage, in which iron 
served as the anode, 11 specimens were used. They were all of 
like proportions, viz, 1: 2%: 4, and were connected two in series on 
115 volts direct current. Condensed data on these tests are 
given in Table 1. All of the specimens behaved in substantially 
the same manner. During the first few hours there was an 
appreciable rise in the external temperature. In most cases this 
rise amounted to from 12 0 to 25 0 C above room temperature as 
measured by a thermometer placed within the electrode if hollow, 
or against the electrode at the point of emergence from the con¬ 
crete and covered with cotton waste if the electrode was solid. 
This rise of temperature usually reached its maximum and dimin¬ 
ished very considerably before any damage to the concrete was 


14 Technologic Papers of the Bureau of Standards 

apparent. After a few hours of current flow bubbles of water 
containing iron rust began to appear around the anode and 
cracks soon developed in the concrete. The manner in which 
the cracking occurred was the same in all specimens. First there 
appeared a very fine crack, beginning at the iron and extending 
outwardly in practically a radial direction. This crack soon 
extended to the outer surface of the concrete cylinder, and then 
gradually widened, while at the same time two or three other 
smaller cracks would appear on the opposite side of the anode from 
the initial crack, also radiating from the center. 

The manner in which these cracks occur and develop is strongly 
^suggestive of a wedge-like action slowly applied at the center of 
the specimen. After the first crack has extended from the center 
to the outer surface of the concrete, the specimen can readily be 
pried open with a screwdriver and separated into several pieces. 
The individual pieces of concrete thus obtained are, however, to 
all appearances as strong as similar specimens of concrete that have 
not been subjected to the influence of electric currents and are 
broken with a hammer with the same difficulty. There is no 
indication whatever that the cement decayed or deteriorated in 
any way, as reported by some earlier investigators, but, on the 
contrary, the appearance of the concrete and its mechanical prop¬ 
erties both indicate very strongly that there has been no such 
action. This is fully substantiated by special experiments de¬ 
scribed in a later section, which appear to show quite conclusively 
that in the body of the concrete remote from either electrode the 
current has no apparent effect on the concrete. 

As shown in Table i, most of the specimens cracked in about 
the same time, the first eight specimens containing Old Dominion 
cement having shown cracks at the end of 23 hours. Nos. 10 and 
11, containing Alpha cement, required 72 hours, while No. 9, made 
with Medusa White Portland cement, required 96 hours to develop 
a fracture. In the latter case, however, it will be noted that the 
voltage at starting was only 24.5 volts, this gradually rising to 54 
volts at the time of cracking. This low voltage at the start was 
caused by the placing of a rheostat in series with the specimen ifi 
order to prevent an unduly rapid rise of temperature. As the 


15 


Electrolysis in Concrete 

specimen warmed up the resistance of the rheostat was cut out by 
steps until full voltage was on. 

The variation of the electrical resistance of the specimen with 
time is of particular interest. In Table i the resistances of the 
test specimens at three stages are given, viz, at starting, at the 
time of cracking, and at the conclusion of the test. It will be 
noted that the first eight specimens containing Old Dominion 
cement show a fair degree of uniformity in initial resistance, the 
average of the eight being 69 ohms. At the end of 23 hours, when 
cracks first appeared, this had increased somewhat, the average 
then being 133 ohms. At the end of the test this average had 
risen to 2194 ohms, or nearly 32 times its initial value. This 
enormous rise in resistance with time is of the greatest importance, 
particularly from the practical standpoint, and is referred to again 
in another part of this paper. 

On breaking open the specimens the embedded iron was found 
to have been very badly corroded, thick layers of scale consisting 
largely of the oxides of iron having formed all over the surface and 
to some extent in the voids in the concrete adjacent to the iron. 
In those specimens which were left in circuit for a long period after 
cracks developed, the deposit of oxides spread for some distance 
out into the cracks, but in specimens 10 and 11, which were re¬ 
moved and opened immediately after cracking, this was not the 
case. Upon breaking open the solid portions of the concrete it was 
found that the discoloration due to the products of corrosion had 
not penetrated into the body of the concrete more than an eighth 
of an inch or so. 

The general appearance of the specimens is shown in Fig. 3, 
which is a photograph of two specimens, one exhibiting the initial 
crack as caused by the passage of the current and the other showing 
the appearance of a similar specimen after having been pried open 
to expose the embedded iron. They form very striking examples 
of what may happen to reinforced concrete when subjected to com¬ 
paratively high voltages. They should not, however, be assumed 
to represent a condition that is liable to be of frequent occurrence 
in practice, as will presently appear. 


16 Technologic Papers of the Bureau of Standards 


TABLE 1 

High Voltage Tests of Reinforced Concrete, Using Iron Electrodes 


Specimen number 

Volts at beginning of | 

test 

Volts at cracking 

Average current to 
cracking (amps.) 

Total ampere hours 

Ampere-hour density 
per sq. in. 

Resistance at begin¬ 
ning of test (ohms) | 

Resistance at crack¬ 

ing 

Resistance at end of 

test 

Hours to cracking 

Hours of test 

Cement used 

Electrode used 

Age of specimen at 

test 

1. 

55.0 

38.0 

0.75 

17.25 

1.04 

64 

90 

1766 

23 

1128 

Old Dom. 

J-inch round 

40 days 




iron 

2 . 

59.0 

78.0 

0.75 

17.25 

1. 04 

70 

171 

2100 

23 

1128 

.do. 

.do. 

Do. 

3. 

59.5 

63.0 

0.57 

13. 20 

0. 86 

79 

157 

2330 

23 

1128 

.do. 

.do. 

Do. 

4. 

54.5 

53.0 

0.57 

13. 20 

0. 86 

72 

132 

1530 

23 

1128 

.do. 

.do. 

Do. 

5. 

56.5 

77.0 

0. 74 

17.02 

0. 63 

66 

140 

2700 

23 

1200 

.do. 

1-inch pipe. 

56 days 

6. 

55.5 

69.5 

0. 79 

18.10 

0. 67 

69 

124 

2400 

23 

1200 

.do. 

.do. 

Do. 

7 . 

55.0 

53.5 

0.57 

13. 00 

0. 48 

58 

119 

1920 

23 

1200 

.do. 

.do. 

Do. 

8. 

62.0 

70.0 

0.74 

17.02 

0.63 

71 

132 

2810 

23 

1200 

.do . 

. do. 

Do. 

9 . 

24.5 

54.0 

0.144 

13. 80 

0. 83 

122 

275 

5250 

96 

3068 

Medusa white 

2-inch round 

Do. 












Portland 

iron 


10. .. 

58. 0 

57. 0 

0. 42 

30. 96 

1 . 08 

100 

140 

140 

72 

72 

Alpha . 

1-inch pipe . 

9 months 

11. 

58.0 

57.0 

0. 39 

28. 20 

1.00 

100 

163 

163 

72 

72 

. do . 

.do. 

Do. 


7. ANODE TESTS ON LOW VOLTAGE 

Tests on specimens subjected to 15 volts and less were carried 
out in much greater number than those on high voltage. At the 
outset of the investigation 90 specimens containing iron electrodes 
were placed in circuit and watched for a period of about 5500 
hours (jpi months), during which time careful records were kept 
of voltage and current flow. Now and then a few specimens 
were broken open to give an idea of what was taking place. At 
the end of the time mentioned a large number of specimens were 
broken open and examined, the amount of the corrosion deter¬ 
mined, and the general condition of the concrete noted. A most 
conspicuous feature of the results of this test, and a very surprising 
one in view of the results previously obtained at higher voltages, 
is the fact that cracking almost universally failed to occur. Of 
the 90 specimens under test only 3 had cracked at the end of 5500 
hours. One of these was made of a white Portland cement, a 
cement which is shown later to give much larger amounts of cor- 












































\ 





















' 



















































































. 

ll : , 






















* 








17 


Electrolysis in Concrete 

rosion under certain circumstances than most of the ordinary 
brands of Portland cement under similar conditions, and the other 
two of Old Dominion cement, to one of which a foreign ingredient 
(20 per cent of paraffin-kerosene solution) had been added. Both 
of the specimens of Old Dominion cement which cracked possessed 
rather unusual characteristics and behaved very differently from 
their fellows of the same composition, inasmuch as their resistances 
at starting were normal, but at cracking the resistance of the one 
to which no foreign ingredient had been added (No. 30, Table 2) 
had increased only three times, while the other had increased only 
two times (see No. 111, Table 15). The time of cracking was 1000 
hours and 2000 hours, respectively. At the end of the test the 
resistance of the first specimen was 6 times as great as at starting, 
while that of the second was 7 times as great. These values are 
but a small fraction of those ordinarily observed at corresponding 
periods in the life of similar specimens, as will later appear. This 
eccentricity seems sufficient to exclude these two specimens from 
consideration as normal specimens. Since white Portland cement 
has been found, in general, to differ very materially from the 
ordinary run of Portland cements in its electrochemical charac¬ 
teristics it should doubtless be considered in a class by itself. 

It seems allowable, therefore, to say that not one of 87 normal 
specimens made of ordinary Portland cement and put under test 
on 15 volts or less had cracked at the end of 5500 hours. Of the 
specimens which were then opened for examination it was found 
that in every case the concrete was broken with difficulty and 
appeared to be as sound as that of similar specimens made at the 
same time and not subjected to the action of electric currents. In 
practically all cases there was more or less corrosion around the 
anode at the point where it entered the concrete and in some 
instances for an inch or so below the surface. In some cases, also, 
where there were voids in the concrete next to the iron there was 
some rust and slight pitting, but in nearly all cases where the con¬ 
crete was in actual contact with the iron the corrosion was quite 
small, and in many cases the iron was practically as bright and 
clean as when placed in the concrete. Condensed data of the 


18 Technologic Papers of the Bureau of Standards 

tests on a few representative specimens broken open to date are 
given in Table 2. It is important to note that the total number 
of ampere-horn's per square inch of embedded electrode surface 
carried, on the average, is considerably larger than the corre¬ 
sponding figures for the high-voltage specimens at the time they 
cracked, the average being 2.3 for the low-voltage specimens, as 
against 0.83 required to crack the high-voltage specimens. It is 
evident, therefore, that the quantity of electricity that passes 
through a specimen does not alone determine the amount of dam¬ 
age that it may do, but that the rate at which the current flows 
is also an important factor. Moreover, it must be evident from 
these observations that the rate at which damage occurs decreases 
with decreasing voltage much more rapidly than the voltage is 
lowered, since in the present instance a reduction of the voltage 
to one-fourth of the value used in the high-voltage tests enabled 
the specimens to run with little or no damage for a period over 200 
times as long as was required to crack and split open the specimens 
on the higher voltage. 

The resistances given in Table 2 are also instructive. It will 
be seen that the average resistance of the specimens at the begin¬ 
ning of the test was 97 ohms, and at the end of the test it had risen 
to 10 200 ohms, or about 105 times its initial value. It is obvious 
that the rise of resistance, and therefore the tendency toward self- 
protection, is much more marked in the case of the low-voltage 
specimens than in those run on the higher voltage. As this mat¬ 
ter is discussed at length later it is simply mentioned here. 


Electrolysis in Concrete 

TABLE 2 

Low-Voltage Tests on Reinforced Concrete Using Ifbn Anodes 


Specimen 

number 

Voltage 

Total ampere-hours 

Ampere-hour density 
per sq. in. 

Resistance in ohms at 
beginning of test 

Resistance at end of 
test 

Hours of test 

Cement used 

Electrode 

used 

Age of 
specimen 
at test 

Corrosion 

12 . 

15 

49.5 

1.81 

75 

10000 

5508 

Atlas 

1 -inrh ninp 


]\Jnnp 

13. 

15 

44.0 

1.61 

! 85 

9370 

5508 

.do 

X liivii A . . 

.do 

ov uayo. . . 

do 

1 , U 11 C 

Do. 

14. 

15 

105.6 

3.84 

64 

3300 

5500 

Dragon 

do 

do 

Slight 

15. 

15 

53.4 

1.95 

75 

21000 

5500 

do 

do 

do 

Do. 

16. 

15 

45.4 

1.66 

94 

3000 

5500 

Alpha 

do 

34 days. 

Do. 

17. 

15 

34.9 

1.28 

81 

50000 

5500 

.do. 

...do . 

do 

Do. 

18. 

15 

55.0 

2.10 

75 

12500 

5500 

Lehigh. 

. .do 

24 days_ 

Do. 

19. 

15 

62.3 

2.30 

69 

15000 

5500 

.do 

.do 

do 

Do. 

20 . 

15 

74.3 

2.73 

100 

5000 

5500 

Pennsylvania.... 

.do. 

23 days... 

Severe 

21 . 

15 

91.0 

3.30 

92 

7500 

5500 

.do. 

.do. 

. .do 

Do. 

22 . 

15 

35.5 

2.10 

141 

8800 

5300 

Giant 

f -inch round 

46 days... 

None 








iron 

23. 

15 

35.2 

2.10 

133 

15000 

5300 

.do. 

. . .do . 

.do 

Do. 

24 7 . 

15 

93.0 

5.60 

127 

1875 

4400 

White Portland.. 

.do. 

57 days... 

Severe 

25. 

15 

66.0 

4.00 

134 

5000 

4400 




Very severe 

26. 

15 

26.6 

0.97 

107 

7500 

1800 

Alpha 

1 -inch pipe.. 

9 months. 

Slight 

27. 

15 

47.6 

1.74 

88 

7500 

1800 

. .do 

.do . 

.do 

Do. 

28 8 . 

15 

52.4 

1.90 

75 

5000 

5691 

Old Dominion... 

.do. 

57 days... 

Medium 

29 8 . 

15 

54.6 

2.00 

75 

5000 

5691 

.do. 

.do. 

...do. 

Do. 

30 9 . 

15 

121.9 

4.50 

81 

469 

2477 

.do. 

. ...do _ 

...do. 

Very severe 

31. 

5 

11.7 

0.43 

126 

5200 

5300 

.do. 

.do. 

80 days... 

None 

32. 

5 

13.7 

0.50 

137 

5700 

5300 

.do. 

.do. 

.. .do. 

Do. 













7 Hours to cracking, 732 . Resistance at cracking, 470 ohms. Ampere-hours per square inch to cracking, 

2.4. 

8 Electrolyte distilled water. 

9 Hours to cracking, 1000 . Resistance at cracking, 260 ohms. Electrolyte distilled water. 

8. TESTS ON MATERIALS OTHER THAN IRON AS ANODE 

(a) COPPER, BRASS, CARBON, AND COPPER-CLAD STEEL 

A number of specimens were made up with Old Dominion cement 
in a 1: 2^: 4 mixture, but using copper, brass, carbon, and copper- 
clad steel as electrodes. Part of these were placed in circuit with 
the metal or carbon as anode, and subjected to voltages ranging 
from 15 to 60 for periods varying from a few days to 10 months. 
The data obtained from the tests on copper, brass, carbon, and 



































































20 Technologic Papers of the Bureau of Standards 

copper-clad steel are summarized in Table 3. Nos. 33 and 34 were 
in series, as also were 35 and 36, and 37 and 38. The action in the 
cases of 33, 37, and 38 was much the same for each one as far as 
appearance went. The resistances at the end were very different, 
however. There was no cracking whatever in any case, nor was 
there any disintegration of the concrete apparent upon breaking. 
The outside surfaces of the blocks were not changed in appearance 
except for the deposit of calcium carbonate usually found beneath 
the water. The action in Nos. 34, 35, and 36 was somewhat 
different. A good deal of water was forced out around the elec¬ 
trode which, evaporating, deposited calcium carbonate, forming 
at the same time a path for the current over the top of the speci¬ 
men which caused deep pits to be formed in the brass rods where 
they entered the concrete. On breaking open the specimens the 
appearance of Nos. 33 to 38 was much the same, there being a 
layer of red copper compound next to the metal, a black layer over 
this, and what was apparently CuS 0 4 diffused for some distance 
into the concrete. Nos. 39 and 40 were the same in appearance 
as 33 to 38, but were not corroded to as great a degree. Nos. 41 
and 42 were in no way different from the rest. 


Electrolysis in Concrete 21 

TABLE 3 

Anode Effects in Concrete using Brass, Copper, and Carbon Electrodes 


Specimen num¬ 
ber 

*o 

*b 

& 

« 

CO 

0 

> 

I 

Volts at end of test 

Total ampere hours 

Ampere-hour density 

per sq. in. 

Resistance in ohms at 

beginning of test 

Resistance at end of 

test 

Hours of test 

33. 

52.5 

8.0 

108.0 

10.1 

55 

920 

3988 

34. 

60.5 

104.0 

108.0 

10.1 

63 

11900 

3988 

35. 

57.0 

57.0 

58.8 

5.3 

112 

15000 

1836 

36. 

57.0 

57.0 

53.6 

4.8 

112 

15000 

1836 

37. 

57.0 

57.0 

103.0 

9.4 

112 

8142 

1836 

38. 

57.0 

57.0 

95.6 

8.3 

112 

8142 

1836 

39. 

15.0 

15.0 

31.6 

3.9 

250 

9370 

5643 

40. 

15.0 

15.0 

42.6 

5.3 

103 

3750 

5643 

41. 

15.0 

15.0 

33.3 

2.0 

115 

3000 

1808 

42. 

15.0 

15.0 

53.4 

3.3 

115 

3000 

1808 

43. 

57.0 

57.0 

75.4 

9.1 

120 

2110 

1302 

44. 

57.0 

57.0 

75.4 

9.0 

116 

2110 

1302 

45. 

58.0 

57.0 

80.5 

7.3 

96 

613 

450 

46. 

58.0 

57.0 

58.0 

5.2 

83 

613 

450 

47. 

57.0 

57.0 

73.5 

6.7 

44 

295 

714 

48. 

57.0 

57.0 

64.9 

5.9 

40 

375 

714 

49. 

15.0 

15.0 

32.3 

3.0 

75 

1875 

3229 

50. 

15.0 

15.0 

52.6 

4.8 

79 

3750 

1919 

51. 

15.0 

15.0 

32.3 

2.9 

101 

3750 

1919 


Electrode used 


J-inch copper. 

i-inch brass. 

.do. 

.do. 

£-inch copper. 

.do. 

f-inch brass. 

§-inch copper. 

|-inch brass. 

i-inch copper. 

f-inch copper-clad 
steel 

.do. 

J-inch carbon. 

.do. 

.do. 

.do. 

.do. 

.do. 

.do. 


Age of 
specimen 
at test 


24 days... 

.. .do. 

7 months. 

...do. 

...do. 

...do. 

50 days... 
...do. 

9 months. 

...do. 

26 days... 

...do. 

10 months 

.. .do. 

5 days.... 

...do. 

50 days... 
10 months 

.. .do. 


CO 

1 

bo 

£ 


8.6 

11.1 


10.0 

1.0 


2.0 

3.5 

10.9 

11.6 


In Nos. 43 and 44, containing anodes of copper-clad steel, the 
greatest amount of corrosion occurred at the bottom of the elec¬ 
trodes and the points where they entered the concrete. The iron 
seemed to corrode very rapidly where it was exposed in cutting. 
Gas forming at the anodes forced water out on top of the concrete 
and made an electrolytic path across the top of the specimen to 
the water in the jar and caused the corrosion where the electrodes 
entered the concrete. There were no pits reaching to the iron 
below the surface of the concrete, except where the iron was ex¬ 
posed in cutting. The surfaces of the rods were much corroded 
and roughened by the action of the current, thereby tending to in¬ 
crease the bond between the concrete and the rod. There was no 























































22 Technologic Papers of the Bureau of Standards 

cracking or disintegration of the concrete notwithstanding the 
high ampere-hour density. On the whole, these specimens acted 
much the same as copper anode specimens, having the same 
layers of oxides in regions outside the exposed area of the iron. 
Specimens 45 to 51 all acted very much the same. The carbon 
disintegrated and appeared as a thick black liquid around the 
electrode to a degree which seemed to depend on the voltage 
and rate of current discharge. There was no disintegration of 
the concrete, nor any sign of cracks in any of these tests, although 
heating was considerable in specimens 45 to 48. The fact that 
the concrete did not crack in any of the above cases is significant, 
and it is interesting to note in this connection that in the case 
of the metals used there is a tendency for the formation of soluble 
salts as the end products of corrosion. Since these salts remain 
in solution to some extent, they diffuse through the concrete and 
thus do not give rise to the local mechanical pressure found in the 
case of iron, where the insoluble oxides are precipitated near the 
surface of the anode. This phenomenon supports the theory that 
the cracking of the concrete is due to a mechanical pressure de¬ 
veloped by the formation of oxides at the anode surface. This is 
referred to again in a later section dealing in detail with the causes 
of fracture in the concrete. 

( b ) TESTS ON ALUMINUM ANODES 

The possibility that the protective film formed over the surface 
of an aluminum-covered rod, when embedded in concrete and 
made anode, might serve as a preventive of electrolysis in concrete 
was first suggested by Magnusson and Smith, 10 and the fact that 
the experimental results published by them tended to show that 
aluminum would not suffer deterioration as iron does when 
maintained anode in concrete led to the following investigation. 

The tests were made on aluminum rods with voltages ranging 
from 5 to 115, the embedded metal being made anode, and, 
although the number of specimens used in each case is rather 
limited, the results may be taken as a fairly reliable indication of 
what may be expected of this metal in service. The specimens 


10 Magnusson and Smith: The Electrolysis of Steel in Concrete, Proc. A. I. E. E., 30, p. 939. 



Electrolysis in Concrete 23 

were all made with Old Dominion cement, the mixture being 
1 : 2% : 4 and all tests were made in tap water. 

The test of specimen No. 52, Table 4, on 115 volts was purposely 
made very severe, in order to see whether the anode film would 
form on aluminum when made anode in concrete, and whether 
it would stand up under the high voltage. The current was very 
high at first, but dropped off rapidly. There was a considerable 
amount of heating in the immediate vicinity of the electrode and 
this may have been primarily responsible for the cracking which 
followed within a few hours. On removal from the jar the specimen 
fell in pieces and a large amount of white aluminum products was 
found around the embedded metal. These products appeared 
to occupy a great deal larger volume than the original metal. The 
concrete was not disintegrated and there was.no dissemination of 
aluminum products through the concrete other than that which 
took place along the cracks. 

Specimen No. 53, made anode on 60 volts, was of somewhat 
faulty construction, as the electrode came to about three-eighths 
inch from the bottom of the cylinder. The film formed, as shown 
in the data in Table 4, but the concentration of current flow at 
the bottom of the rod caused severe corrosion there. The resulting 
pressure from below pushed the rod upward about one-sixteenth 
of an inch and at the same time broke the entire bottom half of the 
specimen into several pieces. The formation of salts was of the 
same nature as in specimen No. 52, but was confined to the bottom 
of the rod. 

Specimen No. 54, made anode on 30 volts, did not crack nor was 
there a marked formation of aluminum salts. The loss by cor¬ 
rosion was very low, as shown in the table, but this was in the 
form of pits which were rather deep, but not of very great area. 
Some of them were one-sixteenth inch in depth and about the 
same diameter. 

Specimen No. 55, made anode on 15 volts, acted almost the 
same as No. 53, except that the loss by corrosion was not so 
great. The construction was the same, however, and such an 
action might have been expected. 


24 Technologic Papers of the Bureau of Standards 

None of the specimens tested for any appreciable length of 
time was free from corrosion of the metal, and where aluminum 
products formed they occupied a much larger volume than the 
metal from which they originated. 

An examination of Table 4 shows that the resistance rises 
very quickly at the beginning of the test when aluminum anodes 
are used. This is doubtless due to the formation of the high- 
resistance film on tbe surface of the aluminum just as in other 
forms of aluminum cells. This resistance is not altogether per¬ 
manent, however, as there was a considerable diminution of 
resistance in most of the specimens as the test proceeded, although 
it never Returned to its initial value. It is not sufficient, however, 
to protect the metal as the large amount of corrosion observed 
shows. 

* TABLE 4 

Aluminum Anodes in Concrete 


Specimen number 

Voltage 
of test 

Hours of 
test 

Resist¬ 
ance at 
beginning 
of test 

Resist¬ 
ance 
after 20 
minutes 

Resist¬ 
ance at 
end of 
test 

Age of 
specimen 
at test 

Loss in 
weight of 
electrode 

Hours to 
cracking 

52. 

115 

20 

57 

1045 

287 

Days 

9 

Grams 

7.136 

10 

53. 

60 

1440 

50 

8000 

7500 

40 

9.2 

192 

54. 

30 

1248 

130 

1700 

8571 

36 

.853 

( u ) 

55.. 

15 

1248 

100 

3000 

3750 

40 

2.4 

192 

57. 

5 

2709 

143 

10000 

20000 

36 

(12) 

( u ) 


11 No cracks. 12 Slight pitting. 


9. CATHODE EFFECTS USING IRON, BRASS, COPPER, CARBON, AND 
ALUMINUM ELECTRODES 

In the preceding section the phenomena noted are those result¬ 
ing when current flows from the embedded iron or other metal 
out into the concrete. When the direction of current flow is 
reversed, making the iron cathode, very different effects are pro¬ 
duced. In this case there is no tendency for the iron to corrode 
because of the current flow, but on the contrary the iron is pro¬ 
tected from any natural corrosion that might tend to take place. 
In the published work of previous investigators no mention is 
made of any injurious effects, either to the iron or the concrete 


















25 


Electrolysis in Concrete 

in those specimens in which the current flowed from concrete to 
iron, except in a single instance in which the specimen cracked. 
The cracking in this isolated instance was beyond doubt merely 
incidental, since all other investigators have failed to note any 
tendency to crack when the iron is made cathode. The conclu¬ 
sion has therefore been widely accepted that when the current 
flows from concrete to iron no effects are produced, and at the 
time these experiments were begun there appeared to be no sub¬ 
stantial ground on which to question this conclusion. It was 
deemed advisable, however, to confirm these observations, and 
accordingly a number of specimens were made exactly similar to 
those used in the anode tests above described, using not only iron, 
but also brass, copper, carbon, and aluminum as electrodes. 
These were placed in circuit with the current flowing from the con¬ 
crete to the electrode. Both high and low voltages were used, 
and the conditions in general were kept exactly the same as with 
the anode tests except for the direction of current flow. Con¬ 
densed data on these tests are given in Table 5. 

TABLE 5 
Cathode Effects 


Specimen 

number 

Volt¬ 

age 

at 

be¬ 

gin¬ 

ning 

of 

test 

Volt¬ 

age 

at 

end 

of 

test 

Resist¬ 

ance 

at 

begin¬ 

ning 

of 

test 

(ohms) 

Re¬ 

sist¬ 

ance 

at 

end 

of 

test 

Total 

am¬ 

pere- 

hours 

Am¬ 

pere- 

hour 

den¬ 

sity 

per 

sq. 

in. 

Hours 

of 

test 

Electrode 

used 

Age of 
speci¬ 
men 
at test 

Cement 

used 

13 56 

15.0 

15.0 

130.0 

150 



144 

J-inch aluminum 

36 days.. 

Old Dominion 

58. 

57.5 

20.0 

67.0 

800 

407.0 

25.4 

8900 

g-inch round iron 

40 days.. 

Do. 

CQ 

58.5 

30.5 

73.0 

950 

395.0 

24.7 

8900 



Do. 

D.f ........ 

£0 

59.0 

17.0 

61.0 

1650 

415.0 

25.7 

8900 

.do. 

.. .do. 

Do. 

61 

52.0 

45.0 

60.0 

2100 

422.0 

26.2 

8900 


.. .do. 

Do. 

62. 

56.0 

96.0 

56.0 

1170 

387.0 

36.8 

3988 

J-inch copper_ 

21 days.. 

Do. 

63. 

57.0 

16.0 

57.0 

195 

387.0 

36.8 

3988 

£-inch brass. 

.. .do. 

Do. 

M 

15.0 

15.0 

53.6 

357 

330.6 

12.2 

5508 

1-inch pipe. 

34 days.. 

Atlas 

fiC 

15.0 

15.0 

53.6 

384 

345.0 

12.8 

5508 


...do. 

Dragon 

00.- . 

66. 

15.0 

15.0 

57.6 

405 

215.0 

8.0 

5508 

.do. 

33 days.. 

Alpha 


is n 

15.0 

57.0 

300 

387.8 

14.3 

5808 


...do. 

Lehigh 

68. 

iJ. v 

15.0 

15.0 

82.0 

468 

263.5 

35.1 

6200 

g-inch copper_ 

50 days.. 

Old Dominion 

69. 

15.0 

15.0 

88.0 

500 

279.4 

36.0 

6200 

g-inch brass. 

...do. 

Do. 

70. 

15.0 

15.0 

75.0 

208 

219.0 

20.7 

3229 

J-inch carbon... 

.. .do. 

Do. 


13 Resistance after 20 minutes, 300 ohms; loss in weight of electrode, 5 grams; hours to cracking, 216. 







































26 Technologic Papers of the Bureau of Standards 

It will be noted that there is a rise in resistance as the test pro¬ 
ceeds very similar to that which occurs in the anode specimens, 
but this rise is less marked, the average ratio of increase being 
about io to i. The first four specimens represented in the table 
(58 to 61) contained iron electrodes. Each one was started in 
series with an anode specimen, and the voltage went down to 
about 9 volts at the end of 1200 hours, due to the relatively 
greater rise of resistance of the anode specimens. The four were 
then connected in series on 115 volts, and the voltage for the 
remaining 7700 hours of the test remained practically constant 
at the values given in the table for the voltage at the end of the 
test. Throughout the test water was forced out around the 
embedded iron and kept the top of the specimen wet. This forc¬ 
ing out of water was evidently due to the formation of gas at the 
cathode, which on escaping forced the water through the pores 
of the concrete to the surface. This water carried calcium hy¬ 
droxide in solution, and as evaporation took place calcium car¬ 
bonate was deposited in rings surrounding the cathode on the 
surface of the concrete. The greater part of the gas evolved 
was hydrogen. As the test proceeded the mortar on the top 
surface of the specimen immediately surrounding the cathode 
became quite soft. This softening extended in the surface to a 
distance of about three-fourths inch from the cathode, and in this 
region the concrete was darker, particularly while wet, than else¬ 
where. After the expiration of several months, and at intervals 
thereafter, certain of the specimens were broken open for exami¬ 
nation. In every case the concrete blocks were broken with 
difficulty, the main body of the concrete being apparently as sound 
as in similar specimens not subjected to the action of electric 
currents. On laying the specimen open it was found that the 
embedded metal was in a perfect state of preservation, but the 
entire region surrounding the cathode for a distance of one-six¬ 
teenth inch to one-fourth inch from the surface of the metal was 
considerably darker in appearance than the main body of the 
concrete and was very soft, like the concrete immediately sur¬ 
rounding the cathode at the surface. The cement here could be 
shaved off with a knife like soft soapstone. 


27 


Electrolysis in Concrete 

In specimens Nos. 62 and 63, having copper and brass cathodes, 
respectively, the same phenomena were observed, except that in 
specimen No. 63 no water was forced out at the surface surround¬ 
ing the cathode. Both cathodes were quite slippery when first 
removed from the concrete. Nos. 64 to 67 contained iron cathodes 
as above, but were subjected to only 15 volts throughout the test. 
The results werfc the same as described above, except that they 
had not advanced quite as far. Specimens Nos. 68 and 69, con¬ 
taining copper and brass electrodes, respectively, behaved ex¬ 
actly the same as Nos. 62 and 63, except that the resulting effects 
were less pronounced. Specimen No. 70 contained an electrode 
consisting of a piece of arc-light carbon. The carbon itself disin¬ 
tegrated badly, and after the bond had been destroyed it was forced 
out of the concrete by the formation of gas underneath. The mor¬ 
tar near the carbon was found to be disintegrated in the same man¬ 
ner and to about the same extent as in the case of metal cathodes 
on 15 volts. 

In all of the above specimens there was a rather sharp line of 
demarcation between the softened area and the remainder of the 
concrete, the soft portion being in every case readily distinguisha¬ 
ble by its darker color. Outside this darkened zone the concrete 
appeared to be as sound as in specimens not carrying current, and 
no physical change of any kind could be detected therein. After 
the specimens had been broken open for some time and allowed 
to dry, the darkened zone became somewhat lighter in shade, but 
there always remained a distinct difference readily detectable by 
the eye. The softening also diminished greatly as the specimen 
became drier, and after becoming thoroughly dry it became nearly 
as hard as the unaffected mortar, but remained distinctly more 
friable. 

Radically different results were obtained from the test on speci¬ 
men No. 56, in which aluminum was made cathode on 15 volts. 
The specimen cracked at the end of 144 hours, and when opened 
the metal was found to be very badly pitted and corroded, but the 
corrosion was different from that found in the anode tests on alumi¬ 
num. The products were black, forming a hard shell around the 
electrode, from which they were separated very readily. This cor- 


28 Technologic Papers of the Bureau of Standards 

rosion was doubtless due to a secondary action of products formed 
by the electrolysis. In the light of the results of experiments de¬ 
scribed further along in this section, it seems quite probable that 
the action is the result of a concentration of alkali metals (Na 
and K) near the cathode by the current with the resulting forma¬ 
tion of sodium and potassium aluminates. The dark color de¬ 
scribed is doubtless due to the presence of iron as impurity. A 
check specimen made at the same time as specimen No. 56, and 
kept in water without current flow, showed no corrosion whatever 
with the exception of a slight reaction between the metal and the 
cement forming a hard layer on the surface of the metal. There 
was no loss of weight in the case of the check specimen. 

10. BOND TESTS OF CATHODE SPECIMENS 

The disintegration of the mortar in the immediate vicinity of 
the cathode, as described above, led to tests on the relative 
strength of the bond where current had passed with embedded 
iron cathode and where it had not. For this test, specimens 58 
to 61 of Table 5 were used, together with four identical specimens 
through which no current had passed. In order to carry out 
this mechanical test the bottoms of the saturated specimens 
were ground over a surface perpendicular to the axis of the em¬ 
bedded iron rods until the lower ends of the rods were exposed. 
The projecting ends of the rods were then sawed down to a length 
of about 2 inches and the specimens placed, one at a time, in an 
Olsen testing machine, which pushed the rods through the blocks 
sufficiently to give the maximum bond strength and also the 
friction load after the bond was broken. The test was carried 
out in the usual way, care being taken to see that the rod was 
perpendicular to the platform of the machine, and the load grad¬ 
ually applied until the beam dropped and slipping commenced. 
The load at which the beam dropped was taken as the maximum 
load of the bond and a succeeding reading made while the rod 
was slipping through the block was taken as the friction load. 
The rod was pushed through the block a distance of about o. 1 inch. 

The results are given in Table 6. It is there seen that the 
passage of current under the conditions of the test carried out 


Electrolysis in Concrete 29 

on specimens 58 to 61 reduced the bond to about one-fifth of its 
original value. 

The electrical test here was quite severe, but the other speci¬ 
mens which were run at voltages ranging from 5 to 15 as described, 
showed on examination that the same disintegrating action was 
going on, and the extent of the softened area, while somewhat 
irregular and slightly indefinite, indicated that at least during 
the first few months of a test the amount of the disintegration is 
probably roughly proportional to the quantity of electricity that 
has passed through the concrete, and is thus but indirectly affected 
by the voltage used, at least within the range of voltages used 
in these tests. In this respect it is in marked contrast to the 
anode effects previously described, which appear to diminish 
much more rapidly than the voltage, until at voltages of 5 to 
10 in the specimens used they practically disappear. 

TABLE 6 
Bond Tests 

[Numbers correspond with numbers in electrical-test record sheet] 

BOND TEST OF CATHODE SPECIMENS, TESTED ON HIGH VOLTAGE 
(50 VOLTS) 


Specimen number 

Total 

load 

Friction 

load 

Maximum 
strength of 
bond in 
pounds per 
square inch 

Friction 
strength of 
bond in 
pounds per 
square inch 

Area of 
embedded 
iron. 


Pounds 

Pounds 



Sq. ins 

58. 

2170 

1200 

127 

70 

17.0 

59. 

2640 

1500 

157 

90 

16.8 


2550 

1270 

155 

77 

16.4 


1300 

1000 

79 

61 

16.4 

Average . 



129 

74 








BOND TESTS ON SPECIMENS THROUGH WHICH NO CURRENT HAD PASSED 


58. 

14500 

7000 

800 

400 

59 . 

‘ 9600 

3800 

585 

231 

60. 

10850 

8800 

711 

516 

61. 

8340 

6000 

496 

357 


Average . 



648 

376 


































30 Technologic Papers of the Bureau of Standards 

11. CAUSE OF SOFTENING ACTION AT CATHODE 

In order to throw some light on the nature and cause of the 
phenomena which gives rise to the softening of the concrete near 
the cathode, a number of experiments were carried out in which 
hollow concrete cylinders were used, made from 1:2^ : 4 concrete, 
using Old Dominion cement, sand, and crushed trap. These hol¬ 
low cylinders were filled with distilled water and immersed in dis¬ 
tilled water in a manner illustrated in Fig. 9. One electrode was 
immersed in the water within the cylinder and the other electrode 
was immersed in the water outside. The cylinders were electro¬ 
lyzed under different conditions, as described below under the 
various experiments. After the flow of current had continued for 
some time the water was drawn off and analyzed. In all cases the 
water contained within the cylinder was taken after the current 
was stopped, and filtered to remove suspended matter before analyz¬ 
ing. The total amount of solution available was about 200 cc, 
and of this one-fourth was used in all cases in each group so that 
the results are directly comparable. 

Sample 1 .—Anode solution from interior of concrete cylinder, 
which had been electrolyzed with an iron anode for 28 hours, with 
15 volts, and a current which averaged about 0.045 amperes. This 
solution contained a light brown precipitate in suspension, due to 
the oxidation of the iron anode. This was filtered off and the solu¬ 
tion was analyzed for S 0 3 , with the following results: S 0 3 , 0.042 g. 

Sample 2 .—Cathode solution from interior of concrete cylinder 
which had been electrolyzed with an iron cathode for 28 hours, 
with 15 volts, and a current which averaged 0.110 amperes. This 
solution was practically clear, with a few suspended particles, 
which were filtered off, and the solution was then analyzed for 
Si 0 2 , A 1 2 0 3 , and CaO, alkalies, and S 0 3 . The solution was 
strongly alkaline. The results of the analysis were as follows: 


Gram 

Si 0 2 . o. 006 

A 1 2 0 3 and Fe 2 0 3 .005 

CaO.003 

K 2 0.446 

Na 2 0. iq6 

S0 3 .None. 








Electrolysis in Concrete 31 

Sample 3 .—Water from interior of concrete cylinder, the same 
as samples 1 and 2, except that no current passed. The water 
remained in the cylinder 28 hours, after which it was practically 
clear, with a few suspended particles, which were filtered off. 
The solution was then analyzed for S 0 3 , Si 0 2 , A 1 2 0 3 and Fe 2 0 3 , 
CaO, and the alkalies, with the following results: 


Gram 

S0 3 .. o. 006 

Si0 2 . None. 

A1 2 0 3 and Fe 2 0 3 . None. 

CaO . None. 

K/).on 

Na 2 0. 006 


Sample 4 .—Anode solution from interior of concrete cylinder, 
which had been electrolyzed with an iron anode for 28 hours, 
with no volts, and a current which averaged 0.82 ampere. This 
solution contained a dark brown precipitate in suspension in con¬ 
siderable amount, caused by the oxidation of the iron anode. 
This was filtered off and the solution was diluted to 250 cc and 
analyzed for S 0 3 , and CaO, with the following results: 

Gram 

S0 3 . O. 061 

CaO. None. 

Sample 5.—Cathode solution from interior of concrete cylinder, 
which had been electrolyzed with an iron cathode for 28 horns, 
with no volts, and a current which averaged 1.8 amperes. This 
solution was strongly alkaline and was practically clear, except 
for a few suspended particles, which were filtered off. The solu¬ 
tion was analyzed for Si 0 2 , A 1 2 0 3 and Fe 2 0 3 , CaO, alkalies, and 
S 0 3 , with the following results: 


Grams 

Si0 2 . 0.027 

A1 2 0 3 and Fe 2 0 3 . 022 

CaO. None. 

K 2 0. i-944 

Na 2 0. 852 

S0 3 . 014 


The solution contained C 0 2 . 

Sample 10A —Cathode solution from interior of concrete 
cylinder, which had been electrolyzed with a carbon cathode 5 
69133°—14-3 
















32 


Technologic Papers of the Bureau of Standards 


hours, with no volts and about i ampere. The solution was 
analyzed for Si 0 2 , A 1 2 0 3 , and Fe 2 0 3 , CaO, alkalies, and S 0 3 , with 


the following results: 

Si0 2 . 

A1 2 0 3 and Fe 2 0 3 . 

CaO. 


Gram 

None. 
None, 
o. 018 


K 2 0.349 

N^O.036 

S0 3 . None. 


Sample 10B .—Anode solution from the exterior of the concrete 
cylinder from which sample 10A was taken. A carbon anode 
was used. This solution was very dark brown, with black sus¬ 
pended particles, due to the disintegration of the carbon anode. 
After filtering the solution was analyzed for S 0 3 with the following 
result: S 0 3 , o. 112 gram. 

The results of these water analyses show that the constituents 
of concrete which are affected by the passage of the electric cur¬ 
rent are the water-soluble constituents, namely, the alkali salts, 
and probably the water-soluble calcium salts, and that the migra¬ 
tions of the ions is the same as in any water solution; that is, the 
positive ions, sodium, potassum, and calcium, move toward the 
cathode, and the negative ions move toward the anode. Thus, 
in samples 1, 4, and 10B, which were the solutions taken from 
around the anode, the S0 3 ions are present in very much larger 
amounts than in sample 3, which was the solution through which 
no current passed, or in samples 2,5, and 10A, which were solutions 
taken from around the cathode; and, further, that the S0 3 content 
was greater in sample 4 than in sample 1, on account of the larger 
current which was employed in the former case. 

In examining the results obtained from the solutions which 
were taken from around the cathode, namely, samples 2, 5, and 
10A, it is found that the solutions were all strongly alkaline and 
that the alkali concentration was very much greater than in 
the case of sample 3, which was the solution in which the concrete 
soaked without the passage of the current. It is also seen by 
comparing samples 2 and 5 with each other that the alkali con- 








Electrolysis in Concrete 


33 


centration was much greater in the latter, due to the greater 
current which was employed. The presence of silica and aluminum 
in these cathode solutions is doubtless to be explained by the 
solvent action of the potassium and sodium hydroxides on the 
combined silica and alumina of the concrete, as will appear later. 
It is seen that more silica and alumina were found in sample 5 
than in sample 2, the former solution being more strongly alkaline 
than the latter. It would be expected that calcium would be 
found in rather large amount in the cathode solutions, as some 
of the calcium is doubtless present in concrete in a water soluble 
condition, so as to be affected by electrolysis; and it will be 
noticed that a slight amount of calcium was found in the cathode 
solutions 2 and 10A, while none was found in solution 3 or in the 
anode solution 4. The reason for there being no calcium in the 
cathode solution 5 is probably found in the fact that any calcium 
which may have been present originally would have been converted 
to the insoluble carbonate, since the solution contained consider¬ 
able amounts of carbon dioxide, probably absorbed from the air, 
and the same explanation may apply to the other cathode solu¬ 
tions, although carbon dioxide was not especially noticeable in 
those solutions. Furthermore, the concrete specimens used in 
these tests had been exposed to the air in the laboratory for more 
than a year before the above tests were made, so it is possible 
that a large proportion of the calcium occurred as insoluble car¬ 
bonate, and hence would not have been affected by the current 
to an appreciable degree. 

Other experiments were carried out along the same line on speci¬ 
mens made up with neat cement, and after they had been sub¬ 
jected to the action of an electric current for several months with 
the embedded iron cathode, samples of cement were taken at 
three points, viz, near the cathode where the cement was soft, 
midway between the anode and cathode, and near the anode, 
and subjected to chemical analysis, the results of which are sum¬ 
marized in Table 6A. The table also contains the results of alkali 
determinations on the cement used in making up the specimens. 


34 


Technologic Papers of the Bureau of Standards 
TABLE 6A 


Specimen from— 

CaO 

k 2 o 

Na 2 0 


Per cent 

Per cent 

Per cent 

Interior around cathode. 

57. 74 

6.41 

1.75 

Between anode and cathode. 

62.20 

.83 

.48 

Nearanode. 

62. 70 

.39 

.18 

Original unset cement. 

62.40 

.87 

.38 


The analyses of both waters and cement, taken as a whole, 
show that potassium and sodium are present in the cement in 
appreciable amounts and that there is a decided tendency for the 
concentration of these to increase in the vicinity of the cathode. 
An examination of the results in Table 6A seems to show that 
at the same time there is a’ decrease in the concentration of the 
calcium near the cathode. This, however, is only apparent. 
The percentage of calcium is expressed in terms of total solids, and 
since there has been an increase in the percentage of potassium 
and sodium in the cathode region the calcium constitutes a rela¬ 
tively smaller portion of the total solids in this region than else¬ 
where in the specimen. 

Since the alkalies are known to react chemically with silicates 
and aluminates, it appeared probable that in such action lay the 
explanation of the effect of the electric current in causing the 
disintegration of the concrete near the cathode. Additional 
experiments were therefore carried out for the purpose of show¬ 
ing whether or not such chemical action might occur in the case 
of Portland cements and what, if any, might be the difference in 
the action of sodium and potassium hydroxides on concrete. For 
these experiments quantities of i : 3 mortar and of neat cement 
were ground to pass a 20-mesh sieve and 5-g samples of each were 
allowed to stand in solutions of sodium hydroxides and potassium 
hydroxides of equivalent strengths for varying lengths of time, 
as given below in detail. The suspended material was then 
filtered off and washed, and the solution was analyzed for Si 0 2 , 
Fe 2 0 3 and A 1 2 0 3 , CaO, and MgO, in order to determine what had 












35 


Electrolysis in Concrete 

been dissolved out by the alkali hydroxides and to ccmpare the 
solvent action of sodium hydroxide and potassium hydroxide. 
The results are tabulated below: 

A.—50 CC OF NORMAL SOLUTION STANDING FOR 18 HOURS 



NaOH 

KOH 

Cement 

Mortar 

Cement 

Mortar 

Si(>2. 

Al203-f-Fe20s. 

CaO. 

Gram 

0. 0005 

None 

Gram 

0.0003 

.0009 

Not determined 

do. . 

Gram 

0. 0011 

.0008 

Gram 

0. 0008 

.0004 

MgO. 








1 


B.—50 CC OF DOUBLE NORMAL SOLUTION STANDING FOR 72 HOURS 


SiO : . 

0. 0023 

0.0016 

0. 0026 

0. 0023 

AbOs+FesOa. 

.0001 

.0006 

.0006 

.0008 

CaO. 

.0234 

.0207 

.0163 

.0349 

MgO. 

None 

None 

None 

None 


C.—50 CC OF 4 NORMAL SOLUTION STANDING FOR 40 HOURS 


Si0 2 . 

Al203+Fe203. 

CaO. 

MgO. 

0. 0126 

.0026 

.0521 

None 

0.0091 

.0010 

.0440 

None 

0. 0131 

.0033 

.0684 

None 

0.0090 

.0032 

.0653 

None 

D.—50 CC OF 10 NORMAL SOLUTION STANDING FOR 6 DAYS 

SiOj 

0. 0992 


0.1003 


A lflOi -I' KPoOv 

. 0211 


.0283 


CaO 

. 4654 


.4336 


MgO 

Not determined 


Not determined 







E.—50 CC OF NEARLY SATURATED SOLUTION, STANDING 6 DAYS (18 NOR¬ 
MAL NaOH AND 15 NORMAL KOH) 


SJO 2 

0.2413 


0. 2224 

A loOo —i— K PoOi 

.0674 


.0668 

CaO 

. 4756 


.4542 

MffO 

Not determined 


Not determined 





















































































36 Technologic Papers of the Bureau of Standards 

These results show that there is a considerable solvent action on 
the silica and alumina in ground mortar and cement by both 
sodium hydroxide and potassium hydroxide, especially in the case 
of the stronger solutions, and that the extent of this solvent action 
increases progressively as the concentration of the alkali increases. 
But there does not appear to be any great difference in the solvent 
action of sodium hydroxide and potassium hydroxide solutions 
which are nearly saturated. The action may be a replacement of 
the calcium silicates and aluminates by sodium or potassium with 
the formation of soluble sodium or potassium silicates and alumi¬ 
nates, and formation of calcium hydroxide. It is doubtful, how¬ 
ever, if, in the above determinations, all the calcium which was 
originally converted to the hydroxide was found in the solutions 
analyzed, because during the prolonged washing which was 
required to get the calcium hydroxide into solution, owing to its 
rather limited solubility in water, some of it was very probably 
converted to the insoluble carbonate by the carbon dioxide of 
the air. 

In another experiment along the same line cylindrical concrete 
blocks, each weighing about 9 kilograms, were allowed to stand in 
solutions of potassium hydroxide and sodium hydroxide of various 
strengths and at the end of three months 50 cc samples of the 
solution were taken from each specimen and analyzed in order to 
determine the relative solvent action that had taken place. The 
strengths of the solutions used and the amounts of silica alumina 
and calcium oxid which were found in solution after three months, 
are given below: 


Solution used 

Amounts dissolved in 50 cc of solution 

Si0 2 

ai 2 o 3 

CaO 


Grams. 

Grams 

Grams. 

One-half per cent KOH. 

0.2 

Trace 

None 

1 per cent KOH. 

.3 

Trace 

None 

4 per cent KOH. 

.8 

Trace 

None 

7 per cent KOH. 

1.3 

Trace 

None 

10 per cent KOH. 

1.9 

0.4 

Trace 

45 per cent KOH. 

15.5 

1.1 

3.4 

45 per cent NaOH. 

5.0 

1.5 

.4 




















37 


Electrolysis in Concrete 

These results also show an appreciable solvent action on the 
silica in the concrete even by the weaker solutions of potassium 
hydroxide, the solvent action becoming greater in the case of the 
stronger solutions; and that slight amounts of alumina were also 
dissolved by the stronger solutions. On comparing experiments 6 
and 7, in which 45 per cent solutions of potassium hydroxide and 
sodium hydroxide, respectively, were used, it is seen that there 
was a markedly greater solvent action on the silica by the potas¬ 
sium hydroxide than by the sodium hydroxide. Furthermore, an 
examination of the concrete block in experiment 6 showed that it 
had been very much disintegrated by the strong solution of potas¬ 
sium hydroxide to a depth of about one-half to 1 inch and could be 
crumbled off very easily; on the other hand, in the concrete block 
of experiment 7, in which sodium hydroxide of still greater strength 
had been used, no such disintegration was apparent on superficial 
examination. It thus appears that potassium hydroxide of great 
strength has a stronger solvent action on the silicia in cement than 
sodium hydroxide of the same per cent composition does, but as 
the strengths of the solutions decrease the solvent actions approach 
the same value. It is probable that the apparent lack of disintegra¬ 
tion reported in experiment 7 came about as a result of comparison 
of the two specimens by physical examination of the surface. It 
should not therefore be taken as indicating that the solvent action 
of sodium hydroxide does not result in disintegration of the con¬ 
crete. That the opposite is true seems to be borne out by the 
results of experiments on cathode specimens to which NaOH had 
been added, which are described below. 

Another series of experiments was carried out in order to find 
if any reaction took place which resulted in leaving the sodium or 
the potassium in the insoluble portion after finely ground neat 
cement had been immersed in sodium hydroxide or potassium 
hydroxide. To this end the alkalies were determined in a 0.5-g 
sample of finely ground neat cement; another 0.5-g sample of the 
same cement was placed in 25 cc of 4n NaOH for six days, after 
which it was filtered off and thoroughly washed and the alkalies 
determined; and another 0.5-g sample was placed in 25 cc of 4n 
KOH for six days, after which it was filtered off and thoroughly 


38 Technologic Papers of the Bureau of Standards 


washed, and the alkalies also determined. The results obtained 
were as follows: 



Original sample 

Sample after being 
placed in 4n NaOH 

Sample after being 
placed in 4n KOH 


Per cent 

Per cent 

Per cent 

K s O. 

0.19 

0.10 

0.12 

NajO. 

.03 

.01 

.01 


The cement used in this test had been exposed outdoors for 
several months, which may account for the small alkali content 
present. The soluble portion was analyzed for Si 0 2 A 1 2 0 3 and 
Fe 2 Q 3 , and CaO with the following results: 



25 cc 4n NaOH and 0.5-g cement 

25 cc 4n KOH and 0.5-g cement 


Gram 

Gram 

SiO,. 

0.0076 

0.0082 

AI2O3 and Fe 2 0 3 . 

.0019 

.0016 

CaO. 

.0938 

.0911 


The results of the alkali determinations on the insoluble por¬ 
tions show that there are no appreciable quantities of insoluble 
compound formed between the sodium or potassium and any of 
the constituents of the cement, since no more alkalies were present 
in the samples which had been placed in sodium and potassium 
hydroxides than in the original sample. The results of the anal¬ 
ysis of the soluble portion were similar to those which were 
obtained before in the other series. 

Another experiment was conducted as follows: A number of 
mortar cylinders 2 > l A inches in diameter by 4% inches long were 
made up with one-half-inch iron rods embedded to a depth of 
4 inches on the axes of the cylinders in a manner similar to that 
shown in Fig. 1. The mortar used was a 1: 2 mix containing Old 
Dominion cement and quartz sand which had been thoroughly 
washed. Distilled water was used in the mixing. A number of 
these cylinders were made up with nothing added, while to others 
potassium hydroxide, sodium hydroxide, and a mixture of equal 
parts by weight of sodium and potassium hydroxides were added 
in various percentages by weight of the cement. After the mortar 































Cathode specimens showing disintegrated mortar about electrode 
















Cathode specimens showing increase of disintegration due to addition of sodium 


















39 


Electrolysis in Concrete 

had set the specimens were placed in jars and connected up with 
the embedded iron cathode (see Fig. 2) and current allowed to 
flow during a period of 62 days. The average current flow was 
about 0.080 ampere under a pressure of 15 volts for each specimen. 
Distilled water served as the electrolyte. At the end of the time 
mentioned above the specimens were all removed from the jars, 
broken open, and photographs taken. Figs. 4, 5, 6, and 7 show 
with remarkable clearness the zone of disintegration and its varia¬ 
tion with varying percentages of the hydroxides as indicated by 
the accompanying cards. By measurement there is, roughly, 
three times as much disintegration where 1 per cent of KOH or 
NaOH is added as where no addition is made. This is approxi¬ 
mately the same ratio as existed between the percentages of alkali 
in the two cases. 

A test was also carried out on some specimens similar to those 
described in the preceding paragraph, from which the sodium and 
potassium contained in the cement had been removed by elec¬ 
trolysis . This electrolytic removal of the sodium and potassium was 
effected by connecting the specimens up with the embedded metal 
anode and allowing a current of about 20 milliamperes to flow dur¬ 
ing an extended period of time. Since the electrode placed around 
the specimen was cathode the sodium and potassium which took 
part in the conduction of the current would in time appear in the 
electrolyte around the cathode as hydroxides or carbonates and 
by changing the electrolyte at suitable intervals all or nearly all 
of the sodium and potassium could be removed. When tests for 
alkalinity of the electrolyte showed that almost no sodium or 
potassium was coming off the current was reversed, making the 
metal embedded in the specimens cathode and carrying a current 
of about 0.050 ampere under a pressure of 30 volts. This condi¬ 
tion was maintained about three months. At the end of that time 
the specimens w r ere broken open for examination. Fig. 7a shows 
the condition of the mortar about the cathode in four of them. 
All of the specimens shown in Fig. 7a were in series while anodes, 
and it is probable that the removal of the sodium and potassium 
was quite complete in the smaller specimens while the larger speci¬ 
mens still contained some of the alkali. The quantity of disinte- 


40 Technologic Papers of the Bureau of Standards 

grated mortar in the case of the larger specimens is but a fraction 
of that found in the specimens shown in Fig. 4, to which no addi¬ 
tions of alkali had been made however, while in the case of the 
smaller specimens no disintegration was evident. The conditions 
under which this result was obtained were practically the same as 
those under which the result shown in Fig. 4 was obtained as far 
as quantity of electricity is concerned. 

It seems fully established, therefore, that the disintegration of 
the mortar at the cathode is due to an accumulation there of 
sodium and potassium by the current and there appears to be a 
consequent liberation by them of the silicates and aluminates of 
the set cement with a formation of soluble products. It is obvi¬ 
ous that this action would continue until all of the sodium and 
potassium in the path of the current had been drawn to the 
cathode. On the other hand, cement free from any appreciable 
quantities of sodium and potassium would not show the disintegra¬ 
tion at the cathode described above. 

12. EFFECT OF ELECTRIC CURRENTS ON THE MECHANICAL STRENGTH 
OF NONREINFORCED CONCRETE 

While the foregoing experiments appear to show quite clearly 
that no effect is produced by the passage of an electric current 
through the main body of the concrete remote from the electrodes, 
it was deemed advisable to corroborate this v T ith a series of mechan¬ 
ical tests on specimens so designed as to eliminate the electrode 
effects. The only mechanical test of this sort that has been pub¬ 
lished was conducted by Magnusson and Smith. 14 Although their 
test was continued but a short time it appeared to show that under 
the conditions of the test there was no appreciable decrease in the 
crushing strength of the mortar. 

In order to secure further information on this subject a test 
was carried out using concrete cylinders 6 inches in diameter and 
8 inches long with no iron embedded. These cylinders were made 
of 1: 2 f/2 :4 concrete, using Old Dominion cement for part of them 
and Alpha for the rest. Sand and crushed trap rock constituted 
the aggregate. After the concrete had become thoroughly set 18 
of the cylinders were provided with electrical connections by 


14 Magnusson and Smith: The Electrolysis of Steel in Concrete, Proc. A. I. E. E., SO, p. 939. 



J 



Cathode specimens showing increase of disintegration due to addition of potassium 





































' 










































Cathode specimens showing increase of disintegration due to addition of sodium and potassium 








































































































































































Electrolysis in Concrete 41 

plastering a 3 by 3 inch carbon plate to the ends of each cylinder 
with cement mortar. A copper lead was attached to each carbon 
plate. The general scheme of the connection is illustrated in 
Fig. 8. When the mortar which held the electrodes on had set 
the cylinders were laid on 2 by 2 inch strips of wood and the 
copper leads connected to the terminals of the 115-volt circuit. 
The potential gradient impressed on these specimens was there¬ 
fore 172 volts per foot and the test was extremely severe. Check 
specimens were placed in the immediate vicinity and all of them 
were thoroughly wet down each day with tap water so that both 
the check specimens and those carrying current were under the 
same moisture conditions. Current flowed continuously for 14 
months and averaged 0.009 ampere for each specimen. This means 



Fig. 8 .—Concrete brick with carbon plates plastered on ends. 


that approximately 75 ampere-hours of electricity passed through 
each specimen under a potential gradient of a little more than 14 
volts per inch. The current density averaged about 0.0003 ampere 
per square inch of cross-sectional area of the specimen. 

At the end of the period of 14 months the specimens were re¬ 
moved from the circuit and tested for their crushing strength. 
The specimens which had been subjected to current were prepared 
for the test by simply splitting off the plaster which adhered to the 
ends. No grinding was required. The testing was done with a 
200000-pound Olsen testing machine. Blotting paper of 7 or 8 
thicknesses was placed on the bottom and top of each specimen in 
order to insure more uniform distribution of press me, and the load 
was run up to a maximum shown by the dropping of the beam when 
the specimen failed. Nearly all of the failures were of such a 





















42 


Technologic Papers of the Bureau of Standards 

character as to show the usual 45 ° shear. The results are given 
in Table 7. There is no indication there that the passage of cur¬ 
rent affected the crushing strength of the concrete. It will appear 
from the first series of tests on specimens made with Old Dominion 
cement that the averages show a slight difference in favor of the 
specimens which carried no current. In the second series, how¬ 
ever, using Alpha cement, the reverse is the case, the difference 
being in favor of the specimens carrying current. The differences 
are negligibly small, however, in view of the wide variation between 
individual specimens subjected to the same treatment. 

TABLE 7 

Effect of Current on Mechanical Strength of Concrete 

SPECIMENS MADE WITH OLD DOMINION CEMENT 


Specimens through which current 
had passed 


173. 

174. 

175. 

176. 

177. 

178. 

179. 

180. 
181. 
182. 

183. 

184. 


Average. 


Crushing 

load 

Specimens not carrying current 

Pounds 


60 630 

185. 

69 210 

186. 

66 910 

187. 

64 060 

188. 

69 700 

189.. . 

53 650 

190. 

41 100 

191. 

66 300 

192. 

69 850 

193. 

73 450 

194. 

92 900 

195. 

31 350 

196. 


197. 

63 260 

198. 


Average. 


Crushing 

load 


Pounds 
73 270 
75 840 
51000 
80 890 

56 210 

57 050 
63 020 
53 490 
65 250 
55 310 
86110 
67 100 
51 210 
88 630 


66 020 


SPECIMENS MADE WITH ALPHA CEMENT 


199. 

47 400 

46 000 

31 450 

50 750 

45 660 

49 300 

205. 

42 000 

35 440 

38 550 

45 040 

200. 

206. 

201. 

207. 

202. 

208. 

203. 

Average. 

204. 

Average. 

45 093 

40 250 





























































Electrolysis in Concrete 43 

The effect of the passage of current on the mechanical strength 
of concrete is further shown to be negligible by a test on speci¬ 
mens similar to the one represented in Fig. 9. Six of these speci¬ 
mens which were made of 112^:4 concrete consisting of Old 
Dominion cement, sand, and crushed trap rock were put under 
the electrical test in the manner indicated in Fig. 2 with the excep¬ 
tion that the inner iron electrode ■ 
was placed loosely in the hole in 
the cylinder. Two of the speci¬ 
mens tested were connected up 
with the inner electrode anode, two 
of them cathode, and the remaining 
two carried no current. The con¬ 
nection was made to the 15-volt 
circuit. Tap water served as elec¬ 
trolyte and care was taken to keep 
the hole on the axis of each cylin¬ 
der full of water. After 454 days 
of current flow the specimens were 
removed from the circuit, the ends 
ground off parallel with each other, 
and the specimens tested in the 
same way as the specimens de¬ 
scribed in connection with Table 7. 

Condensed data are given in Table 8. 

There is no indication in the results 
that the passage of current affected 
the crushing strength of the concrete 
to an appreciable degree. This test in tests t0 show the bcalion of the rise of 
was a severe one, the potential gra- electrical resistance of concrete specimen, 
dient being about 7 volts per inch due to flow of current 
and the concrete in a condition of saturation. The conditions 
were also such that the electrode products were free to act on the 
concrete and the absence of any appreciable depreciation in the 
crushing strength of these specimens is very significant. 


























44 


Technologic Papers of the Bureau of Standards 
TABLE 8 

Effect of Current on Mechanical Strength of Concrete 


Specimen number 

Time of test in 
days 

Average current 
in amperes 

Ampere-hours 

passed 

Total crushing 
load 

209. 

454 

0.013 

144.0 

36 000 

210. 

454 

.014 

151.3 

36 780 

212. 

454 

.054 

591.7 

35 370 

213. 

454 

.043 

468.0 

47 080 

214. 

454 

0 

0 

36 430 

215. 

454 

0 

0 

50 000 


13. CAUSE OF CRACKING OF REINFORCED CONCRETE BY ELECTRIC 

CURRENTS 

As regards the various theories that have been advanced as to 
the cause of cracking of reinforced concrete which were previously 
mentioned in this paper, the first, that of gas pressure, appears 
to have little evidence to support it. In all cases it has been 
found that a much greater volume of gas is liberated at the cathode 
than at the anode, and if the pressure due to any accumulation of 
gas within the concrete were an important factor in causing the 
cracking, we should expect to find even greater damage in cathode 
specimens than in anode specimens. On the contrary, however, 
the cracking is found to be peculiarly an anode effect, and it 
therefore seems certain that gas pressure at most plays but a 
very minor part in causing the damage. As for the second theory, 
that of heating, the same objection applies, because the heat 
developed in the cathode specimens is substantially the same as 
in the anode specimens under similar conditions. Moreover, 
cracking has been repeatedly produced in anode specimens in 
which the external temperature rise was but a few degrees (12 0 
to 15 0 C), whereas equal and much greater heating in cathode 
specimens (ioo° C in one case) failed to cause fracture. It must 
be admitted that heating of the embedded iron, if sufficiently 
great, is capable of developing cracks in concrete, but with the 
ordinary circumstances under which cracking has occurred in the 
laboratory this is not sufficient to contribute materially to the 
damage, as the cathode experiments show. 















45 


Electrolysis in Concrete 

The third theory, that of electrochemical decomposition of 
the cement, also appears to rest on very uncertain ground. The 
fact that the main body of the concrete remains unaffected, and 
at the anode where cracking always originates, no deterioration 
of the concrete is evident, argues strongly against this theory. 
It is seen that the concrete is unquestionably weakened by chemical 
action in the region very near the cathode, but the fact that no 
cracks develop there, even under the weakened conditions, is 
proof positive that the immediate cause of the cracking resides 
elsewhere than in a chemical action similar to that which occurs 
at the cathode. The results of the chemical analyses given in 
the section immediately preceding this one show that the products 
formed by the reactions at the cathode are soluble and hence 
could not give rise to an internal pressure which could cause 
cracking similar to that observed in anode specimens. More¬ 
over, the disintegration of concrete by an increase in volume 
through chemical reactions within the mass with resultant insolu¬ 
ble products always takes place by crumbling. The cracking of 
anode specimens is in marked contrast to this as described here¬ 
tofore. It appears inevitable therefore that we must conclude 
that the cracking is a direct result of some process occurring at 
the surface of the anode, and hence we must look to the anode 
phenomena for the true explanation of the damage. The explana¬ 
tion previously advanced that the cracking is due to the deposi¬ 
tion of oxides of iron between the surface of the iron and the con¬ 
crete, which, occupying a larger volume than the original iron, 
produces a mechanical pressure sufficient to crack the surrounding 
concrete, appears on the surface to be well founded. There are, 
however, no published data showing that such pressures actually 
develop or indicating what magnitudes they may attain. On 
the contrary, the results of experiments by Barker and Upson 15 
of the University of Vermont with so-called collapsible electrodes, 
in which cracking of the concrete was observed, have caused 
those investigators to oppose this theory and to hold that no 
pressure of any considerable magnitude is necessary at the surface 

15 Barker and Upson: Experimental Studies of the Electrolytic Destruction of Reinforced Concrete, Eng. 
News, 66, p. io. 



46 Technologic Papers of the Bureau of Standards 

of the iron anode in order to produce cracking of the concrete. 
There appears, however, to be some question in regard to the 
strength of these collapsible electrodes, made by rolling sheet 
iron into cylindrical form. Certain electrodes of this type used 
in the present investigation showed somewhat surprising rigidity, 
due either to the open edges becoming bound by the concrete or 
by cementation of overlapping surfaces accompanying corrosion 
of the iron. It was therefore deemed advisable to carry out 
additional experiments with a view of furnishing further infor¬ 
mation. 

(a) EXPERIMENTS WITH SPECIMENS CONTAINING LOOSE ELECTRODES 

In order to determine whether cracking would occur without 
actual contact between the anode and the concrete some speci¬ 
mens were made up as shown in Fig. 9. These are substantially 
of the same form as those previously used except that the anode 
instead of being cast solidly in the concrete is inserted loosely 
in a cylindrical hole in the center of the concrete cylinder, there 
being a space of about half an inch between anode and concrete 
on all sides. This space was filled with water to complete the 
electrical circuit, and the specimens were then connected to the 
circuit in the usual way, the iron being anode. In this case we 
have all the possibilities for chemical action, heating, and the 
formation of deposits of oxides within the mass of the concrete, 
but it is impossible for any mechanical pressure to develop between 
the iron and concrete. Specimens of this kind were put under 
test on 15 and no volts, the former being in circuit for more 
than a year, without the least trace of cracking or other deteriora¬ 
tion having developed. This affords strong additional evidence, 
if any were needed, that heating or chemical action have no im¬ 
portant part in the destruction of the concrete in anode speci¬ 
mens under ordinary conditions. Its chief value in this con¬ 
nection, however, lies in the fact that it shows that in the absence 
of direct mechanical pressure between the iron and the concrete 
the cracking does not take place. 

(ft) EXPERIMENTS WITH CARBON ELECTRODES 

Experiments with carbon electrodes in which there can be no 
secondary reactions to cause swelling of the anode also confirm 


47 


Electrolysis in Concrete 

this view. (See also Table 3, specimens 45 to 48.) Some 
specimens were made up with carbon electrodes as shown in 
Fig. 8. Rectangular blocks of concrete 4 inches square by 8 
inches long were made and after being allowed to set small plates 
of brush carbon with copper leads attached were plastered on 
each end by means of neat cement. These specimens were then 
connected to the 115-volt circuit and after having been in circuit 
for more than 14 months showed no sign of fracture. Here, 
again, all conditions such as gas pressure, heating, and chemical 
action, and in fact all the conditions which have been supposed 
to contribute to the destruction of the concrete are present, with 
the single exception of the possibility of the development of me¬ 
chanical pressure, and the failure to occur of cracking or disin¬ 
tegration of the specimens is significant. 

(c) EXPERIMENTS WITH COLLAPSIBLE ELECTRODES 

It is not sufficient, however, to show merely that cracking does 
not take place in those cases where mechanical pressure is absent. 
It is necessary to show that a mechanical pressure actually is 
developed when cracking occurs, and that this pressure is of 
sufficient magnitude to produce the phenomena observed. In 
order to definitely demonstrate this point the following experi¬ 
ments were carried out: 

The first test was made on a standard size specimen of 1:2 
mortar made up with a collapsible electrode such as is shown in 
Fig. 10. The sheet iron of this electrode was rolled to as true 
a cylinder as possible under the circumstances and wrapped at 
intervals with fine copper wire. When the electrode was em¬ 
bedded in the specimen the mortar worked into the seam at a 
thus forming a brace for the edge of the sheet iron at that point. 
After setting the specimen was placed in circuit on 50 volts, 
carrying a current which varied from 1.2 to 0.37 amperes as the 
test proceeded. 

After 96 hours the specimen was found to be cracked. The 
crack formed at c and extended radially to the edge of the speci¬ 
men. The sheet iron was forced away from the mortar about 
one thirty-second inch from a in a clockwise direction around to 
c, making it evident that there had been some pressure developed 


69133°—14-4 



48 


Technologic Papers of the Bureau of Standards 


between the concrete and the iron. The iron being braced at a, 
however, would not yield in the other direction, and since any 




Fig. 10 .—Collapsible electrode. 


further relaxation would have to take place completely around 
the electrode, it is probable that the friction became too great 
and the specimen cracked. 










































































































































































♦ 


















' 














- 












































































































































Fig. 11 .—Specimens used in tests to determine the force produced by the corrosion of iron 

in concrete 






49 


Electrolysis in Concrete 

In order to test this matter further two more specimens were 
made up with collapsible electrodes of the same material as the 
first, but with a curved strip of sheet iron covering the seam, as 
shown at e, in order to prevent binding of the edges by the con¬ 
crete. These two specimens were placed in series on 115 volts 
and continued in circuit for three months. The current was 
never greater than 1 ampere nor less than 0.045 ampere during 
that time. There was evidence of a great deal of corrosion, but 
no cracks appeared in either of the specimens, although the voltage 
was about 60 to 70 volts for one specimen and 45 to 55 volts for 
the other. 

These conditions are so severe that similar specimens with 
solid electrodes would inevitably have cracked within a day or 
two. A thick layer of oxide was deposited between the sheet- 
iron cylinder and the cement, which caused considerable shrink¬ 
age of the cylinder, and it was without doubt this yielding of the 
cylinder which relieved the pressure and prevented cracking of 
the concrete. 

(d) MEASUREMENT OF FORCE PRODUCED BY CORROSION OF IRON IN CONCRETE 

Another and more striking experiment to demonstrate the 
existence of a mechanical pressure and at the same time to give 
an idea of the order of magnitude of the forces developed was made 
with the apparatus shown in Fig. 11. Several sections of 4- 
inch cast-iron pipe about 5 inches long were cut through on one 
side with a hack saw, making slits about one-sixteenth inch in 
width. These sections of pipe were then filled w T ith concrete 
and an iron rod embedded in the center of each to serve as one 
electrode. After being properly aged, the specimens were con¬ 
nected in circuit, with the outer cast-iron sleeves as anodes. In 
that case corrosion would take place on the inner surface of the 
cast iron and produce a layer of oxide between the iron and the 
concrete. If any considerable pressure were produced it would 
result in a tendency to expand the cast-iron sleeve, with conse¬ 
quent widening of the slit. This actually proved to be the case. 
Fig. 11 shows on the right one of these cylinders as it first appeared 


50 Technologic Papers of the Bureau of Standards 

and on the left one that has undergone considerable expansion. 
The increase in the width of the slit in this instance is about 
three thirty-seconds inch. As the cast-iron sleeve was about 
one-half inch thick and possessed considerable rigidity, a very 
appreciable mechanical pressure is here made evident. Calcula¬ 
tion showed that the natural expansion of the concrete could not 
have produced more than a few per cent of the effect observed. 

A modified form of the last experiment was next carried out, in 
which provision was made for actually measuring in a rough way, 
the magnitude of the pressure developed. A hollow cast-iron 
cylinder shown in Fig. 12 of 1 inch internal diameter and 2 inches 
external diameter, and ifA inches in height was cut through on one 
side with a hack saw, making a slit one-sixteenth inch in width. 
On either side of the slit three thirty-seconds-inch holes were 
drilled three-sixteenths inch deep and iron pins inserted with 
projections of one-eighth inch. These were placed opposite each 
other and filed flat on the outside with such a pitch that if the 
cylinder opened out appreciably there would be no difficulty in 
measuring the distance between the outside of the bases of oppo¬ 
site pins with a flat vernier caliper. 

To find the radial pressure required to produce a given amount 
of spreading of the slit in the cylinder, two piano wires were 
wrapped once around the cylinder and a varying load applied to 
one end of the wires while the system was suspended from the 
other end. The cylinder was greased and although the friction 
between the wires and the cylinder would doubtless still be quite 
great a little agitation seemed to cause the deflection, or narrowing 
of the slit, to be almost directly proportional to the load as shown 
in the curve in Fig. 13. Also the external radial load required to 
produce a given narrowing of the slit would be nearly the same as 
the internal radial load required to produce the same widening. 

A three-fourths-inch solid iron cylinder was placed in the hole 
in the cast-iron cylinder and the space between them filled with 
1:1 cement mortar made up with a 1 per cent NaCl solution. The 
object of adding the salt was to increase the rate of corrosion and 
shorten the time required to make the test. The bottom of the 



Fig. 12 .—Specimen used in test to determine the force produced by the corrosion of iron 

in concrete 

























f 











































Electrolysis in Concrete 51 

specimen was covered with two layers of asphalt and felt to keep 
the current from shunting around the mortar while under test 
the test being made in a crystallizing dish filled to one-eighth 
inch from the top of the shell with lime water to prevent the mor¬ 
tar from drying out and at the same time keep the pins from 
rusting seriously. 

The specimen was put in circuit on 15 volts January 2, 1912, 
with the iron cylinder as anode, the distance between the bases 



Pounds 10 20 30 40 50 60 70 80 90100 120 140 160 180 200 220 240 260 280 300 

Kgm 9.1 18.2 27.3 36.4 45.5 54.6 63.7 72.8 81.9 91.0 100 109.2 118.3 127.4 136.5 

LOAD ON WIRES 


Fig. 13 

of the pins having previously been measured. On January 12 
the specimen was removed from circuit, measured for total deflec¬ 
tion of the pins, and the central electrode removed. The measure¬ 
ments were then taken again to obtain the permanent set. The 
difference between the total deflection and the permanent set rep¬ 
resents the true deflection over which the ratio of deflection to 
load or internal radial pressure is probably constant. As seen 
from the calibration curve of Fig. 13, the load required to give a 
deflection of 0.0022 cm is 30 pounds. This load corresponds to a 





































































52 Technologic Papers of the Bureau of Standards 

radial pressure of 40 pounds per square inch on the interior of the 
shell where the diameter is 1 inch. This is obtained from the 
formula Pdl = 2 TN, or external load equals internal load, and 
where 

P = internal radial pressure, 
d = interior diameter of shell, 

1 = length of shell, 

L = load on wires and 
N = number of wraps of wire arotmd shell. 

This is neglecting friction, but since in the actual experiment 
the friction of the rough, corroded surface on the mortar was 
beyond doubt much greater than the friction of the wires on the 
oiled surface of the cylinder, the error, if any, would probably 
tend to make the calculated pressure due to oxidation too low 
rather than too high. It is therefore safe to assume that the 
actual pressure developed is as great as the value given below. 

Substituting L = 30 pounds, and the value for the dimensions 

2 x 

of the shell in the above formula we have P = ——-=40 pounds. 

I X 1.5 

N = 1 since in reality the two wires constitute but one wrap 
around the shell. 

The deflection of 0.0022 cm for a pressure of 40 pounds per 
square inch corresponds to an internal diameter of the shell of 1 
inch. Making up the specimen with the three-fourth inch elec¬ 
trode and filling the space surrounding it in the bore with mortar 
as described above had the effect of increasing the radial pressure 
per square inch required for the same deflection in the ratio of 1 to 
three-fourths. The pressure at the surface of the electrode would 
be, therefore, 53 pounds per square inch. That is, 53 pounds per 
square inch over the surface of the three-fourths inch electrode 
would produce the same deflection as 40 pounds per squasre inch 
exerted upon the walls of the tube. 
































Pig 14 —Form of specimen used to determine the force produced by the corrosion of iron in concrete 








Electrolysis in Concrete 53 

TABLE 9 

Calibration and Test Data on Cylinder for Measuring Pressure Caused by 
Corrosion of Iron 


Load. 

Deflection in set of 
pegs No. 1 

Deflection in set of 
pegs No. 2 

Deflection in set of 
pegs No. 3 

Average 

First calibration: 

cm 

cm 

cm 

cm 

Lbs. 0.Kgm 0.. 

0 

0 

0 

0 

33.15.. 

0.004 

0.005 

0.006 . 

0.005 

59.26,8.. 

.006 

.007 

.008 

.007 

86.39.1.. 

.008 

.007 

.010 

.008 

110.50.0.. 

.010 

.011 

.012 

.011 

Second calibration: 





0.0 .. 

0 

0 

0 

0 

40.13.2.. 

.006 

.006 

.004 

.006 

74.33.6.. 

.008 

.008 

.006 

.007 

100.45.5.. 

.010 

.010 

.010 

.010 

125.56.8.. 

.012 

.012 

.010 

.011 

149.67.8.. 

.013 

.014 

.012 

.013 

172. 78.2.. 

.014 

.014 

.016 

.015 




Permanent set 

.002 

Test data: 

cm bet. pins 

cm bet. pins 

cm bet. pins 

cm def. 

Jan. 2,9:00. 

0.268 

0.947 

0.986 

0 

2, 4:00. 

.872 

.990 

1.028 

0.043 

3, 9:00. 

.916 

1.034 

1.072 

.088 

4, 9:00. 

.952 

1.068 

1.106 

.122 

6, 4:00. 

1 .011 

1.124 

1.162 


8, 4:00. 

1. 012 

1.127 

1.168 


9, 9:00. 

1.020 

1.134 

1.174 


12,1:00. 

1.068 

1.180 

1.220 

Current 0.045 amp. 

After removal of cen¬ 




cm 

tral electrode. 

.960 

1.076 

1.116 

True def. .105 


The data of Table 9 show a true deflection of 0.105 cm, which 
corresponds to a radial pressure of 2400 pounds per square inch 
at the surface of the electrode, mostly due to the formation of rust. 

As a check on the foregoing experiment a similar cast-iron shell, 
inches in external diameter, was made up as shown in Fig. 14. 
This cylinder was slotted lengthwise at opposite extremities of 
a diameter to a depth one-sixteenth inch less than the thickness 
of the shell. The thickness of the shell was one-fourth inch in this 
case, so the cuts were each three-sixteenths inch deep, leaving a 








































54 Technologic Papers of the Bureau of Standards 

thickness of one-sixteenth inch of cast iron holding the two halves 
of the shell together on either side. The object in making slots of 
this character in the shell was to cause practically all of the elon¬ 
gation of the iron due to an internal pressure to take place in the 
slot. The smaller cross sectional area of iron there would then 
reach its elastic limit sooner than the thicker portion and lead to a 
quick break in the event of the pressure becoming great, while a 
shell one-sixteenth inch in thickness throughout might expand to 
such an extent that a break would not occur. A three-fourths- 
inch solid-iron electrode was cemented in the bore of the shell with 
i :i mortar made up with a 3 per cent NaCl solution. After the 
mortar had set the shell was put in circuit on 15 volts with the 
central electrode anode. In about three days the two halves of 
the shell were found to be broken apart by the formation of rust on 
the surface of the anode. By measuring the length of the shell 
and the width at different points of the broken portion on the side 
which evidently yielded first, data were obtained from which a 
curve was plotted and integration showed the area of the broken 
section of iron to be 0.106 of a square inch. The formula which 
expresses the relation between the internal load due to radial 
pressure within a cylinder which is required to rupture it and the 
resistance of the cylinder against the rupture is Pdl = 2 AF where 

P = internal radial pressure per unit area, 

A = cross-sectional area of iron on one side of cylinder, 
d = internal diameter of cylinder, 

1 = length of shell and 
F = breaking strength of cast iron. 

As in the former case the internal diameter of the shell is to 
be taken as the diameter of the electrode and for the same reason. 
Assuming F to be 20 000 pounds per square inch (d = ^ inch) 
we have, solving for the internal radial pressure, 

P =- o ~7 5 x ' i""5 - = ^ P oun( * s P er S( l uare inch. 

In a similar specimen tested in the same way, but having an 
area of iron on each side of 0.131 square inch holding the two 



55 


Electrolysis in Concrete 

halves of the shell together, the break occurred at 4700 pounds 
pressure per square inch, calculated in the same way. 

While, of course, the above measurements are only approxi¬ 
mate, a higher degree of accuracy does not appear to be necessary, 
since we are not chiefly concerned with the actual pressure de¬ 
veloped, but desire only to know whether or not it can become of 
sufficient magnitude to destroy concrete. The above experiments 
are sufficient to show that the force developed due to.the corrosion 
of iron in concrete by electric currents may reach a value of at 
least several thousand pounds per square inch, which is amply 
sufficient to produce the fractures observed in reinforced concrete 
blocks under the influence of electrolysis. 

14. RISE OF ELECTRICAL RESISTANCE OF REINFORCED CONCRETE DUE 
TO FLOW OF CURRENT 

The electrical resistance of concrete is a factor of great impor¬ 
tance, but one which varies so greatly with varying physical condi¬ 
tions, especially with varying moisture content, that it is difficult 
to give any reliable numerical values except in the case of approxi¬ 
mately saturated specimens. An average figure for representa¬ 
tive specimens of thoroughly wet concrete may be taken as 
varying from 4000 to 6000 ohms per centimeter cube, depending 
somewhat on the proportions. With reduced moisture content 
the resistance rises rapidly, the concrete becoming a fairly good 
insulator when thoroughly dry. 

(a) RISE OF RESISTANCE OF ANODE SPECIMENS 

In the published work of previous investigators mention is 
frequently made of the fact that when electric current passes 
through reinforced concrete, under the conditions usually imposed 
upon it in the laboratory, there is a gradual increase of resistance 
with time, regardless of the direction of flow of current. Nothing 
definite has been said as to the probable cause of this rise of 
resistance, nor does it appear that its importance as a factor in 
minimizing trouble from electrolysis in reinforced concrete has 
been fully appreciated. With a few exceptions, which are con¬ 
sidered later, such a rise of resistance occurred in all of the sped- 


56 Technologic Papers of the Bureau of Standards 

mens tested in the course of this work. When the specimens 
were first placed in circuit the resistance was a minimum, but 
upon the application of the electric current the resistance began 
to rise. In the low-voltage specimens the first apparent increase 
in resistance may have been more or less affected by polarization, 
but in the higher voltage tests at 15 to 100 volts polarization 
effects are negligible. The resistance at first increased quite 
rapidly, but the rate of increase usually commenced to diminish 
after about 1000 to 1200 hours. The rise of resistance continued 
for a period varying from several days to several months, accord¬ 
ing to circumstances as described later, until an approximately 
constant condition was reached. In the case of higher voltages 
the increase of resistance was the more rapid at first, but the 
rate of increase was not maintained in proportion to the voltage 
applied, so that a greater ampere-hour flow of current was required 
to produce a given rise of resistance in the case of high-voltage 
specimens than where the voltage was low. Typical curves 
showing the resistance as a function of time and also as a function 
of the ampere hour flow of current are shown in Figs. 17, 18, and 
19. The relative magnitude of the initial and final resistances 
varied very much under different conditions, but the general 
tendency was the same whether the specimens were run as anode 
or cathode on high or low voltage. The results of the tests for 
anode effects on low voltage, which are summed up in Table 2, 
show an average increase of resistance to 105 times the original 
value at the end of 5500 hours. The results of the tests for 
cathode effects on all voltages, which are summed up in Table 5, 
show an average increase to 10 times the original resistance at 
the end of about the same period. The anode tests on high 
voltage do not show such a large increase of resistance as the 
anode tests on low voltage, but this is due, no doubt, to the fact 
that, owing to the early destruction of the specimens on high 
voltage, these tests were of comparatively short duration. 

(6) DETERMINATION OF LOCATION OF RISE OF RESISTANCE 

A rise of resistance of sufficient magnitude to cause the reduc¬ 
tion of current through a specimen of reinforced concrete to less 
than 1 per cent of its original value was recognized as a phenome- 


57 


Electrolysis in Concrete 

non of great importance and was therefore given special con¬ 
sideration. The first step taken in determining its nature was 
the very obvious one of finding its location; that is, ascertaining 
whether it is an anode or a cathode effect, or both, or is dis¬ 
tributed throughout the specimen. After the first unsuccessful 
attempts in this direction, the follow¬ 
ing experiment was devised and car¬ 
ried out. Fig. 15 shows the general 
form of the specimen used. It was of 
standard type, made of 1:2 mortar, 
with a three-fourths inch round-iron 
electrode embedded in the axis of the 
cylinder. The contact piece shown 
embedded at B in the figure consisted 
of two concentric sheet-iron cylinders 
which were perforated with a large 
number of one-half-inch holes. These 
holes were so spaced as to remove 
about one-third of the area of the iron 
and when the cylinders were in place, 
one within the other, the holes were 
opposite. Rubber covered copper wire 
leads were soldered to each cylinder. 

The inside of the outer cylinder and 
the outside of the inner cylinder were 
painted with an alkali resisting metal 
preservative having considerable tem¬ 
porary insulating value so that when 
the cylinders were shoved together the 
outer and inner faces of the arrange¬ 
ment were conducting but were insu¬ 
lated from each other. The whole was embedded concen¬ 
trically with the central iron rod and mortar worked into 
the holes. When current was made to flow through the speci¬ 
men from the central to the outer electrode the mortar in the 
holes provided a path for it in passing out of the cylinder B. 



Fig. 15 .—Spe men used in experi¬ 
ments to determine the location of the 
rise of resistence of concrete speci¬ 
mens due to flow of current. 





















OHMS 


58 Technologic Papers of the Bureau of Standards 

No current could flow through B itself. The purpose of this 
was to prevent corrosion of the sheet iron and a consequent 

1300 

1200 

1100 

1000 

900 

800 

700 

600 

500 

400 

300 

200 

100 



0 5 10 15 20 25 30 35 40 45 50 


DAYS 
Fig. 16 


possible changing of the resistance between the faces of the 
contact piece and the concrete and also to prevent polarization of 
the surface of the cylinder B. 




































































Electrolysis in Concrete 


59 


When the mortar had set the specimen was placed in tap water, 
allowed to stand until its resistance became fairly constant, 
and then connected up on 15 volts, direct current, with the central 
electrode anode, using the usual sheet-iron cylinder for the outer 
electrode C. Current was allowed to pass continuously except 
for about 33 horns each week. The following measurements 
were made at regular intervals: 

(1) Total current and voltage from A to C in the figure. 

(2) Potential fall by potentiometer from A to B and B to C. 
The inner face of the contact piece B was used for the measurements 
A-B and the outer face for B-C. 

(3) Resistance by alternating current from A to C. Calcu¬ 
lating the resistances A-B, B-C, and A-C from the observed data, 
and plotting the values obtained in each case as a function of 
time, gives the curves of Fig. 16. The result indicates that in 
this type of specimen at least the rise of resistance occurs almost 
wholly in the neighborhood of the cathode. 

The next step taken was to select specimens from those under 
test which had been in circuit for a year or more, and thoroughly 
stir the electrolyte in which they were immersed. That finished, 
the outsides, i. e., the surface adjoining the cathode of the speci¬ 
mens, were scraped with a sharp-edged tool. The results are 
given in Table 10. 

TABLE 10 

Effect on the Resistance of Anode and Cathode Specimens of Scraping 
the Outside Surface of the Concrete 


Specimen 

number 

Proportions 
of concrete 

Cement used 

Added 

Hours in 
circuit 

Voltage 

Resist¬ 
ance at 
beginning 
of test 

Resistance 

before 

disturbing 

water 

71. 

1:2. 5:4 

Old Dominion.. 

20% crude oil No. 

5600 

15 

131 

17400 




4147 





72. 

1:2.5:4 

.do. 

20 % oil par. sol- 

5600 

15 

160 

25820 

73. 

1:2. 5:4 

.do. 

20% oil No. 4147... 

5600 

15 

208 

861 

74 

1:2. 5:4 

Atlas. 


5500 

15 

76 

8000 

75 

1:2. 5:4 

Old Dominion . 


0 

0 

157 

157 

7fi 

1:2.5:4 

.... do. 


6000 

15 

75 

5000 

1 



























6o 


Technologic Papers of the Bureau of Standards 
TABLE 10—Continued 


Specimen number 

Resistance 
after stirring 
water with 
current on 

Resistance 
after scraping 
outer surface 

Resistance 
after stand¬ 
ing in air 
nine days 

Polarity of 
embedded 
electrode 

Electrolyte 

Age of 
specimen 
at test 

71 . 

12000 

14000 

861 

Not stirred.. 

380 

1026 

861 

Not scraped. 


Positive. 

Tap water... 

60 days 

Do. 

Do. 

46 days 

8 months 

57 days 

72 


.do. 

73. 


Negative.... 

Positive. 

Tap water... 

.do. 

74 

1400 

75. 

Neutral. 

.do. 

76. 


196 


Positive. 

.do. 







As shown by this table, specimen No. 71 lost about 30 per cent 
of its resistance on stirring the electrolyte, and returned nearly 
to its original resistance after scraping the outside to a depth of 
about one thirty-second inch. The indications are that by suffi¬ 
ciently diligent scraping the resistance could have been reduced 
still more. No. 72 lost about 50 per cent of its resistance on stir¬ 
ring the electrolyte. It was not scraped to as great a depth as 
No. 75, but was worked down with a hoe-shaped tool while in the 
jar with current flowing. No. 73, in which the central electrode 
was cathode, was not changed in resistance in the least by stirring, 
scraping, or otherwise disturbing it. No. 74 was removed from 
the jar after measuring its resistance and allowed to stand in air 
for nine days. At the end of that time it was returned to the 
electrolyte, allowed to become saturated, and another measure¬ 
ment made of its resistance which was found to have fallen to 
about one-sixth of its maximum value. Specimen No. 75 had 
been standing in water for eight months with no current passing. 
Measurement showed that there had been no appreciable increase 
of resistance. No. 76 was tested in distilled water, but did not 
act differently from the rest. Scraping had the same effect on its 
resistance as on that of Nos. 71 and 72. 

(c) CAUSE OF RISE OF RESISTANCE 

The results given above indicate quite clearly that the greater 
part of the rise of resistance in specimens with embedded anodes 
takes place near the cathode and it is quite probable that it is due 
to several causes. Analysis of the concrete scraped from the 






























Electrolysis in Concrete 


61 


surface of an anode test specimen after having been in circuit a 
year shows that there is a large accumulation of calcium carbonate 
at this point which undoubtedly has its share in the increase of 
resistance. This accumulation takes place as a result of a con¬ 
centration of Ca(OH) 2 near the cathode surface by the current 
where it comes in contact with C 0 2 absorbed by the water from 
the air with the resulting precipitation of CaC 0 3 within the pores 
of the concrete near the surface of the specimen, thua plugging up 
these pores and forming a nearly impermeable wall. If a specimen 
is made anode for a considerable time, it shows a tendency to 
decrease in weight while the resistance is increasing, whereas, if 
the current is reversed, it regains a considerable portion of the 
loss. This indicates that electrical endosmose, or the carrying of 
the water bodily toward the cathode through the pores of the con¬ 
crete by the current, may also have something to do with the 
increase of resistance by drying out the specimen in this way. If 
the current is reversed rapidly, say at a rate of two reversals per 
second, an action is observed that is much like the rectifying 
action of an aluminum cell but is much slower because at 120 
reversals per second it disappears entirely, no reading being ob¬ 
tained on a direct-current instrument placed in the circuit. The 
larger current flows when the embedded metal is cathode. The 
difference between anode and cathode resistance with two reversals 
of current per second may be as great as 30 per cent in a new 
specimen, decreasing very much, however, with a specimen which 
has been in circuit long enough to attain a high resistance. No 
explanation is offered for this action. It is probable that the 
three phenomena above mentioned all contribute to the rise of 
resistance, but to what extent each contributes, and what other 
actions may also occur, can not be stated at present. 

(d) RISE OF RESISTANCE OF CATHODE SPECIMENS 

In case the embedded electrode is made cathode a rise of resist¬ 
ance occurs which is, however, much less than when the embedded 
electrode is anode. This might be expected from the fact that 
C 0 2 has very little access to the Ca(OH) 2 at the surface of the 
embedded electrode, and hence the tendency to produce a dense 
precipitate of CaC 0 3 would be very slow. Moreover, electrical 


62 Technologic Papers of the Bureau of Standards 

endosmose would have a tendency to fill the pores with water in¬ 
stead of drying them out. In fact, there is good reason to believe 
that the rise of resistance which takes place at the embedded cath¬ 
ode is due chiefly to the liberation of gases at that point by the 
electrolysis of water; and since these gases are necessarily slow 
in escaping through the pores of the concrete, the electrolyte is 
largely excluded from the pores near the cathode surface with con¬ 
sequent rise in resistance. This is indicated by bubbling and forc¬ 
ing out of water around the cathode, by variations of the resistance 
of such specimens of as much as io to 20 per cent while current is 
flowing, and also by the fact that’the resistance drops back quite 
close to its original value when the current is discontinued for a few 
days and the gas permitted to diffuse. Specific instances are given 
below as examples: A standard type specimen of 1:2.5 14. concrete, 
made up with Alpha cement and containing a i-inch pipe for an 
electrode, had an initial resistance of 60 ohms. After being in 
circuit on 15 volts with the central electrode cathode for 2200 hours, 
the resistance had reached a value of 300 ohms. On leaving the 
current off for a week the resistance decreased to 136 ohms. An¬ 
other specimen of the same character as the above, with the excep¬ 
tion that it was made up with Giant cement, had been in circuit 
1000 hours as cathode on 15 volts. The resistance had risen from 
120 to 240 ohms. The current was left off for about a week and 
the resistance decreased to 125 ohms, or practically to its original 
value. A third case was that of four cathode specimens in series 
on 116 volts. These specimens were of 1:2.514 concrete, made 
up with Old Dominion cement, and containing three-fourths-inch 
round-iron electrodes. The resistance of the four specimens in 
series at the beginning of the test was 256 ohms. After 4162 hours 
the resistance had increased to 2700 ohms. The current was then 
cut off for about four days. When it was resumed the resist¬ 
ance was found to be 865 ohms, or about four times the original 
resistance. 

Some very interesting curves are shown in Figs. 17, 18, and 19. 
One of the curves of Fig. 17 is a plot of the current values as a 
function of time for a high voltage anode specimen, and the other 
the same for a low voltage anode specimen. These curves cover 


Electrolysis in Concrete 63 

the first 1000 hours of each test. It is seen that the greatest drop 
of current occurs during the first 200 hours. If the current is then 
discontinued for a considerable time the resistance decreases 
almost to its original value; this is partially shown in the curve 
of the high-voltage specimen at the point where the current is 
indicated as having been off for a short time—an hour or two at 
most. Beyond the 200-hour point the curves are both compa¬ 
rable with a straight line and nearly parallel. This is also shown to 



some degree in the curves of Fig. 18. These show plots of resist¬ 
ance as a function of time for a high and a low voltage anode 
specimen, respectively. The high-voltage specimen was con¬ 
tinued in circuit but a short time in comparison with the low- 
voltage specimen, but there is an indication that the curves would 
be very nearly parallel if they had both been continued in circuit 
indefinitely. Fig. 19 shows plots of increase of resistance as a 
function of ampere hours for high and low voltage specimens. 
If the continued increase of resistance after the initial rapid 
69133°—14 - 5 











































































64 Technologic Papers of the Bureau of Standards 

increase were wholly an electrical effect and its rate of increase 
depended on the rate of ampere hour discharge we should expect 
the two last-named curves to practically coincide. There is a 
wide divergence, however, showing that the increase of resistance 
is not wholly an electrical effect. A much larger amount of elec¬ 
tricity passes on the high voltage for a given rise of resistance than 
on the low voltage. It would thus appear that lapse of time is 
an important factor in the rise of resistance noted. As seen from 



HOURS 

Fig. 18 

the results obtained on specimen No. 75, however, the mere passage 
of time without current flow has but little effect, a fact which is 
proved more fully by measurements made on a number of other 
specimens in the course of the work. The foregoing phenomena 
are entirely in accord with the explanation of the rise of resistance 
set forth above. 

(<) EFFECT OF THE ADDITION OF SALTS ON THE RESISTANCE OF CONCRETE 

A notable exception to the practically general rule with regard 
to the increase of resistance of reinforced concrete when current 














































































65 


Electrolysis in Concrete 

flows through it will now be considered. A not uncommon prac¬ 
tice in connection with the placing of concrete in cold weather is to 
dissolve 2 or 3 per cent of common salt (NaCl), or calcium chlo¬ 
ride (CaCl 2 ), in the water which is used in making the mortar. 
This is of material benefit in lowering the freezing point of the 
mixture while setting. It is not definitely known that it has any 
detrimental effect upon the concrete itself. The effect of this 
addition of salt to concrete upon its electrical properties appeared 



Fig. 19 


very important, and hence several tests were made in the usual 
manner with salt added in various ways. In all cases where such 
specimens were tested as anodes the damage was not only found 
to be very much hastened, but instead of the usual increase of 
resistance with passage of current, the resistance actually decreased 
in some cases as the test proceeded. Two specimens in particular 
which were made up with no addition of salt, but which were tested 
in a 3 per cent salt solution decreased from 115 ohms to 80 ohms 














































































66 Technologic Papers of the Bureau of Standards 

and from 130 ohms to 60 ohms at the end of 410 hours and 1490 
hours, respectively. (See specimens 126 and 127, Table 15.) 

A second test, in which the concrete was made up with a 10 
per cent salt solution and tested as anode on 15 volts over a 
period of five days, showed a decrease of resistance of 25 per 
cent. Cathode specimens tested in a manner similar to the 
tests on the first two specimens mentioned showed an increase 
of resistance of 20 to 25 per cent in the same length of time. This 
marked difference in character from that of all the other speci¬ 
mens tested in this work must be attributed chiefly to the salt, 
or rather to the presence of an excessive amount of the acid 
radical chlorine. The currents taken by the specimens were 
rather high in most cases, and hence heating may have had some¬ 
thing to do with the decrease of resistance instead of an increase, 
but it can not account for all of it. In tests on specimens to 
which no salt was added the temperature rise was nearly as 
great, but the rise of resistance never failed to occur. 

The failure of the resistance of the concrete to rise when a large 
amount of sodium chloride is added may be explained in part by 
the fact that, owing to the relatively great concentration of the 
sodium ions as compared with the calcium ions in this case, the 
greater part of the current is carried by the sodium, and hence 
little calcium is carried to the surface. A more important factor, 
however, is that the presence of sodium chloride in a solution 
tends to prevent the precipitation of calcium carbonate at ordi¬ 
nary temperatures, and thus the plugging up of the pores can 
not occur. This phenomenon is, therefore, corroborative of the 
explanation above given for the rise of resistence of specimens of 
normal concrete. 

(/) RISE OF RESISTANCE OF CONCRETE BURIED IN DAMP EARTH 

It is evident that a rise of electrical resistance of reinforced 
concrete takes place under all the conditions of the electrolysis 
experiments conducted in the laboratory except when an appreci¬ 
able amount of chlorine, or perhaps other acid radical, is present 
in the cement. These laboratory conditions provide a liquid 
electrolyte in all cases. In practice wet soil would more often 


6 7 


Electrolysis in Concrete 

be the electrolyte if conditions were favorable to electrolysis. 
Current would also be likely to flow between sections of reinforce¬ 
ment without leaving the concrete. In order to determine 
whether or not a rise of resistance would occur in the case of 
concrete in soil, two blocks of concrete containing embedded iron 
were molded in holes dug in the earth so that about 3 inches of 
the block projected above the surface. The blocks were of 1:25:4 
concrete, 3.5 feet square by 2.5 feet deep. Four electrodes were 
embedded perpendicularly to a depth of 2 feet in each block, 
with 4 or 5 inches of each one projecting for electrical contact 
purposes. These electrodes consisted of i-inch iron rods, i-inch 
iron pipe, and a length of 4-inch wrought-iron pipe. The blocks 
were placed about 2 feet apart. Three of the eight electrodes 
were connected to the negative terminal of the 15-volt circuit 
and the remaining five to the positive terminal. Current flowed 
continuously except for about 33 hours each week. Part of the 
current which flowed to the positive electrodes flowed out through 
the surface of the blocks to the soil and to a large ground plate 
near by, which was connected to the negative terminal of the 15- 
volt circuit. The rest returned by way of the electrodes which 
were connected to the negative terminal of the 15-volt circuit. 
Current readings were taken on each electrode from time to time. 
The values of the current on each electrode are plotted as a func¬ 
tion of time in Figs. 20 and 21, the first figure being for the anodes 
and the second for cathodes. A rise of resistance was found to 
take place, but it is a longer time in appearing than in the case 
of specimens tested in jars. 

(g) RISE OF RESISTANCE OF CONCRETE SETTING IN AIR 

A similar test was carried out by passing current through three 
reinforced concrete beams 5 inches square by 5 feet long. These 
beams were made up of 1:2^214. concrete and reinforced with 
one-fourth-inch rods. Four rods were embedded about i }4 inches 
from the bottom of each beam and came to within 1 y inches from 
the ends. In two of the beams 1 foot of length on the end of 
each rod was bent up until the end of the rod came to about 1 ]/ 2 
inches from the top surface of the concrete. In the other two 


68 Technologic Papers of the Bureau of Standards 

the rods were laid flat. The four beams were placed with their 
ends on planks so they were insulated from the earth. Holes 
5 inches square were cut in the sides of a number of sheet-iron 
cylinders and the ends of three of the beams inserted, the fourth 
being used as a check. The cylinders were then filled with wet 
earth and connected to the 15-volt circuit, so that each beam, 
with the exception of the check specimen, was under 15 volts 
pressure over its full length with wet earth conducting the current 



from the sheet-iron cylinder to the end of the beam. Current 
readings were taken from time to time and the values obtained 
are plotted as a function of time in Fig. 22. The rise of resist¬ 
ance occurs in much the same manner as in the blocks buried in 
the earth. 

In order to gain some information as to the specific resistance of 
concrete while setting in air without current flowing, eight 1: 2 l /i : 4 
concrete specimens were made in the form of rectangular blocks 
similar to the one shown in Fig. 28. In each of the specimens two 




































































Electrolysis in Concrete 


69 


perforated sheet-iron plates were embedded transversely at a dis¬ 
tance of 8 inches from each other and 2 inches from the ends of 
the block. These plates were used as contact pieces for measuring 
the resistance of the portion of the concrete block between them. 
The dimensions of the plates were equal to those of the cross- 
sectional area of the block in which they were embedded. The 
perforations mentioned above constituted about one-third of the 
area of the plates and enabled the mortar of the different parts of 



the block to unite through the plate, thus holding the parts firmly 
together. When the blocks were removed from the molds the 
electrical resistances between the plates were measured by alter¬ 
nating current, using the Kohlrausch bridge. 

The specimens were then buried in damp sand for about eight 
weeks. On removal from the sand the resistances were measured 
again, after which the specimens were placed in air in the labora¬ 
tory and the measurements repeated from time to time. The 
average results are olotted as a function of time in Tig. 23* The 






























































70 Technologic Papers of the Bureau of Standards 

points do not fall on a smooth curve, but this can doubtless be 
attributed to the state of the atmosphere with regard to moisture 
content at the time the measurements were made. The weight of 
the specimens remained nearly constant from the time of removal 
from the sand to the end of the test. This can best be accounted 
for, in view of the large increase of resistance noted, by the fact 
that with the slow-setting process which goes on during the first 
few months of the life of concrete a considerable amount of 



water is taken up by hydration, enough, possibly, to counteract 
the drying effect of the atmosphere. 

It is therefore seen that a great rise of resistance takes place 
under conditions practically identical with those occurring in 
practice, and it is, therefore, an important factor in reducing dam¬ 
age to concrete structures, and particularly so in the case of mod¬ 
erate or low voltages, as a few volts or less, such as would almost 
invariably be met with under actual conditions. Its magnitude 
is such as to increase by many times the life of a structure over 















































































Electrolysis in Concrete 71 

what it would be if subjected to severe electrolysis conditions 
and the rise of resistance did not occur. 

15. VARIATIONS IN THE MAGNITUDE OF ELECTROLYTIC CORROSION 
OF IRON IN CONCRETE 


It is well known that in cases of corrosion by electric currents 
the total amount of corrosion does not in general correspond with 
Faraday’s law, but is in many cases considerably less than the 



Fig. 23 


theoretical amount. In particular, in the case of concrete, it was 
to be expected that the actual amount of corrosion would be less 
than that expected from Faraday’s law, because of the alkalinity 
of the electrolyte. This obviously has an important bearing on 
the subject of electrolysis in reinforced concrete, because the 
extent of the reduction in the amount of corrosion determines the 
damage which will result to the reinforcing material by a given 
ampere discharge, and also determines in greater or less degree 
the extent of the injury to the concrete itself. This subject is here 






















72 Technologic Papers of the Bureau of Standards 

discussed under two heads, i. e.: (i) Corrosion of iron in normal 
concrete, and (2) Corrosion of iron in concrete to which certain 
foreign ingredients had been added. 

The first data on electrolysis of iron in concrete that admitted 
of comparing the theoretical amount of corrosion which should 
have occurred at the anode with that which actually did occur 
were obtained by Glauber and reported on by Prof. Langsdorf 16 
in 1909. The results were very indefinite but showed that the 
amount of corrosion actually obtained and that which should 
have been obtained according to Faraday’s law did not agree, the 
observed corrosion being only a fraction of the theoretical. In 
the terms of Faraday’s law the theoretical amount of metal which 
will dissolve from an iron anode in an electrolyte, a solution of 

ferrous sulphate, for instance, is g per ampere-hour where 

n is the change of valency. If the change of valency is 2, as it is 
in nearly all ordinary cases, the amount of iron dissolved per 
ampere-hour would be 1.045 g- However, if the proper condi¬ 
tions are not maintained in the cell while the process of electrolysis 
is going on, or if an alkaline solution is used, a quantity of metal 
considerably less than the theoretical may be dissolved, that 
portion of the electricity passed in excess of what is used in dis¬ 
solving the iron being consumed in breaking up the electrolyte. 
The quantity of metal actually dissolved divided by the theoretical 
amount according to Faraday’s law is called the “efficiency of 
corrosion,” which, as stated above, was shown by the data in 
Langsdorf’s report to be in certain cases at least but a few per 
cent. 

The next work along this line was done by Burgess 17 two years 
later. The data obtained by him were more definite and con¬ 
firmed the earlier observations. Iron pipe was used in the experi¬ 
ments and the corroded metal was “ scratch bushed ” after remov¬ 
ing it from the concrete in order to free it from rust and ascertain 
the loss in weight. The greatest efficiency of corrosion shown in 
any case not involving the addition of chemicals to the cement or 

16 A. S. Langsdorf: Electrolysis of Reinforced Concrete, Jour. Assn, of Eng. Soc., 42 , p. 69; 1909. 

17 Abstract of paper by C. F. Burgess: Electrolytic Corrosion of Iron in Concrete, Eng. Record, 63 , p. 373; 
1911. 




Electrolysis in Concrete 


73 


electrolyte was 6.88 per cent. From this value it varied down¬ 
ward to 1.05 per cent, depending in some degree, apparently, 
upon the mixture of the concrete and also on whether it was 
made “moist” or “wet” in mixing. The latter conditions would 
undoubtedly affect the percentage of voids. Testing some speci¬ 
mens in a 3 per cent salt (NaCl) solution gave the rather surprising 
result of increasing the efficiency of corrosion to percentages 
varying from 55 to 80. The exactness of the results in general 
was open to some question, however, because a considerable 
amount of natural corrosion could easily have taken place on the 
interior of the pipe during the test and the method used for clean¬ 
ing the pipes, which was by brushing, would necessarily give rise 
to some uncertainty. The experi¬ 
ments were of great value, however, 
for the purpose for which they were 
intended, viz, to point out the general 
tendencies involved. 

(a) CORROSION TESTS USING DIFFERENT 
CEMENTS 

By way of verification of the fore¬ 
going results a number of tests were 
carried out using different cements, 
and every effort was made to have 2 "mortar cubes used in efficiency 
the conditions of the tests as nearly 0F C0RR0S,0N TESTS - 

uniform as possible. The specimens Flg * 24 

used consisted of 2-inch cubes of 1:2 mortar made up wet with 



standard Ottawa sand and distilled water. A round iron elec¬ 
trode, one-fourth inch in diameter by 2^ inches long, was em¬ 
bedded 1 inches deep in each cube, as shown in Fig. 24. Before 
embedding these electrodes they were filed to a bright surface 
and a short bare copper wire soldered to each one. This was 
followed by weighing them on a balance having a sensibility of 
0.0005 g, the average weight of the anodes being about 14 g. 
In order to prevent natural corrosion of the exposed portion of 
the electrode while the specimen was immersed in distilled water 
undergoing the setting process, this exposed portion was painted 
with two coats of an alkali-resisting preservative paint. 













74 Technologic Papers of the Bureau of Standards 

After the setting process had continued for approximately two 
weeks the test was commenced. Each specimen was placed in 
a crystallizing dish 5 inches in diameter by 2 inches deep and 
surrounded by a sheet-iron cylinder, which served as the cathode. 
The dish was then filled to within one-fourth inch of the top 
of the cube with distilled water, and the specimen put in circuit 
on 15 volts with the central electrode anode. The current den¬ 
sity averaged about 0.025 ampere per square inch of anode 
surface at the beginning and gradually decreased to about 0.005 
ampere per square inch at the end of the test. Current flowed 
continuously with the exception of 33 hours each week, current 
readings being taken at intervals, which increased as the test 
proceeded. When cracking occurred, or, if cracking did not 
occur, as soon as a sufficient number of ampere-hours had passed 
to give a reliable indication of the efficiency of corrosion, the 
specimens were removed from the circuit and broken open. The 
corroded electrodes were cleaned by a process hereafter described 
and then weighed and the losses determined. The current read¬ 
ings were plotted as a function of time, and the area included 
between the axes and the curve integrated by means of a plani- 
meter. The area of the curve and the scale to which it was drawn 
gave the number of ampere-hours which had passed through the 
specimen; multiplying by 1.045 gave the amount of corrosion 
which would have occurred if the iron had dissolved in accordance 
with Faraday’s law. Dividing the theoretical amount into the 
amount observed gave the efficiency of corrosion as defined above. 
Table 11 contains the condensed data. 

TABLE 11 


Efficiency of Corrosion in Various Cements 


Specimen 

number 

Name of cement 

Volt¬ 

age 

Am¬ 

pere- 

hours 

Am¬ 

pere- 

hour 

density 

Anode 

loss 

Theo¬ 

retical 

loss 

Effi¬ 
ciency 
of corro¬ 
sion 

Hours to 
cracking 

77 . 

Alpha. 

15 

3.95 

3.1 

Gram 

0.085 

Gram 

4.11 

Per cent 

2.07 

1.12 

202 

202 

78. 

.do. 

15 

2.72 

2.1 

.032 

2.84 

79 (check) 19 ** . 

80 . 


0 

0 

0 

.001 

0 

Dragon. 

15 

2.44 

1.92 

.047 

2.54 

1.85 

202 




















Electrolysis in Concrete 


TABLE 11—Continued 

Efficiency of Corrosion in Various Cements—Continued 


Specimen 

number 

Name of cement 

Volt¬ 

age. 

Am¬ 

pere- 

hours 

Am¬ 

pere- 

hour 

density 

Anode 

loss 

Theo¬ 

retical 

loss 

Effi¬ 
ciency 
of corro¬ 
sion 

Hours to 
cracking 






Gram 

Gram 

Per cent 


81. 

Dragon. 

15 

1.94 

1.53 

.040 

2.03 

1.97 

202 

82 (check) 19 **.. 


0 

0 

o 

o 

o 

9. 

Old Dominion. 

15 

7.7 

1.3 

.046 

8.0 

' 0.57 

No cracking 

10 . 

.do. 

15 

7.7 

1.3 

.068 

8.0 

0.85 

Do. 

11. 

.do. 

15 

7.7 

1.3 

. 118 

8.0 

1.47 

Do. 

12. 

.do. 

15 

7.7 

1.3 

.223 

8.0 

2.80 

Do. 

83. 

.do. 

15 

0.99 

0.78 

.054 

1.03 

5.20 

42 

84. 

.. ..do. 

15 

1.16 

0.91 

.079 

1.22 

6.40 

66 

85 (check) 19 *.. 

.do. 

0 

0 

0 

.003 

0 

86. 

Lehigh. 

15 

1.57 

1.23 

.084 

1.64 

5.10 

90 

87 . 

.do . 

15 

1.54 

1.21 

.061 

1.61 

3.79 

90 

88 (check) 19 **.. 

.do . 

0 

0 

0 

.004 

0 


89 . 

Universal 18 . 

15 

0.43 

0.34 

.073 

.455 

16.00 

24 

90 . 

.do . 

15 

0.42 

0.33 

.058 

.437 

13.20 

24 

91 (check 19 **).. 

.do . 

0 

0 

0 

.004 

0 


92 . 

Vulcanite . 

15 

4.83 

3.80 

.017 

5.04 

0.33 

No 

93 . 

.do . 

15 

5.74 

4.52 

.023 

6.00 

0.38 

Cracks 

94 (check) 19 **. . 

.do . 

0 

0 

0 

0 

0 



95 . 

Erz cement 19 . 

15 

1.52 

1.20 

.237 

1.58 

15.00 

193 

96 . 

.do . 

15 

1 . 58 

1.24 

.160 

1.65 

9.70 

193 

97 (check) 19 **.. 

.do . 

0 

0 

0 

.001 

0 













18 Containing 0.3 per cent SO3. 

19 Manufactured in Hemmoor, Germany. 
i9a These specimens carried no current. 


The test of each cement was made on a set of three cubes, one 
being kept without current as a check on natural corrosion and 
the other two tested electrically, as described. The results ob¬ 
tained from specimens of Old Dominion cement include those of 
four 3 by 4 inch cylinders of 1.2 mortar with one-half inch rods 
embedded. 

The check specimens showed very little natural corrosion, the 
losses in these cases being hardly greater than the errors which 
would be expected to occur in weighing. The efficiencies of cor¬ 
rosion compare very well with those obtained by Burgess, and 
show beyond a doubt that under the conditions of these experi¬ 
ments but a small fraction of the current passing through a speci¬ 
men of reinforced concrete is effective in dissolving the iron. 
The variations in efficiency of corrosion between different cements 


















































j6 Technologic Papers of the Bureau of Standards 

are quite marked; the corrosion efficiency of some specimens of 
Old Dominion and Lehigh being three or four times that of Alpha 
and Dragon. The Vulcanite shows a remarkably low efficiency of 
corrosion, but while under test the resistance of the specimens 
was less than half that of the other specimens. The Universal 
cement contained only 0.3 per cent S 0 3 , no calcium sulphate being 
added in grinding the particular batch from which the specimens 
were made. The Erz cement shows a comparatively high effi¬ 
ciency of corrosion. This cement contains a relatively large per¬ 
centage of iron, the iron replacing part of the aluminum which 
enters into the composition of ordinary Portland cement. 

An examination of the chemical analyses of these cements 
shows that there is apparently no relation whatever existing be¬ 
tween the variations in the efficiency of corrosion and the S 0 3 
content of a cement. 

(b) EFFECT OF TEMPERATURE ON EFFICIENCY OF CORROSION 

One of the most important facts to be noted in connection with 
the efficiency of corrosion in concrete is the great change in the 
efficiency of corrosion attendant upon a change of the voltage 
through a wide range of values and the consequent accompanying 
change of current density at the surface of the electrode. There 
is evidence of this change in the efficiency of corrosion in the 
results of the anode tests described in the first part of this paper. 
The high voltage tests recorded in Table 1 show that cracking of 
the specimens occurred after an ampere-hour density of 0.83 per 
square inch had passed through them. Specimens Nos. 10 and 11 
of Table 1 were in such a condition at the end of the test with 
regard to natural corrosion of the exposed iron as to permit clean¬ 
ing and weighing to determine the loss by electrolysis. No. 10 
showed an efficiency of corrosion of 37 per cent and No. 11 of 40.8 
per cent. There is a marked contrast between these values and 
those found in Table 2, where the results of testing specimens on 
15 volts are recorded. The 15-volt specimens passed an average 
of 2.32 ampere-hours per square inch of anode surface with no sign 
of cracking, excepting 3 isolated instances out of 90, the charac¬ 
teristics of which were such as to exclude them from consideration 


Electrolysis in Concrete 


77 


as normal specimens. The electrode of specimen No. 25 of Table 2 
was undoubtedly corroded more than that of any specimen re¬ 
corded there. It was cleaned and weighed and the efficiency of 
corrosion found to be 10 per cent. From this extreme value of 
10 per cent for a 15-volt specimen the efficiencies of corrosion for 
this voltage varied downward, decreasing nearly to zero in many 
cases. Specimens Nos. 31 and 32 of Table 2 were tested on 5 
volts. At the end of 5300 hours 0.43 and 0.53 ampere-hours per 
square inch of anode surface had passed. When broken open 
there was no sign of corrosion whatever. For specimens of the 
same form the various current densities were in practically the 
same ratio as the voltages at like periods of the tests. The 
decrease in the efficiency of corrosion therefore does not take place 
in the same proportion as the decrease in current density. For the 
type of specimen used in these tests and for the conditions of the 
tests it seems that corrosion practically ceases at a voltage some¬ 
what below 15 volts. 

An additional experiment, which shows the effect on the effi¬ 
ciency of corrosion of varying the voltage and current density was 
carried out on specimens from the same group of 2-inch mortar 
cubes as 87 and 88 of Table 11. These specimens were tested in 
the same way as those of Table 11, excepting that the voltages on 
the different specimens varied from 1 to 15 volts. Condensed 
data of the tests are given in Table 12. 

TABLE 12 

Efficiency of Corrosion with Various Current Densities 


Specimen 

number 

Name of cement 

Voltage 

Ampere- 

hours 

Anode 

loss 

Theoretical 

loss 

Efficiency 
of cor¬ 
rosion 

Average 
amperes 
per square 
inch 

QR. 

Lehigh. 

1 

0. 00034 

Gram 

0.002 

0 

Per cent 

0 

0 

99 . 

.do. 

1 

. 00034 

.001 

0 

0 

0 

100 

_ do. 

4 

1.15 

.015 

1.20 

1.25 

0.0022 

101 . 

.do. 

6 

1.74 

.031 

1.82 

1.70 

.0034 

102 . 

.do. 

9 

2 . 28 

.085 

2.38 

3.57 

.0049 

1 ft? ... 

.do. 

11 

1.40 

.116 

1.46 

8.00 

.0075 

104. 


15 

1.57 

.084 

1.64 

5.10 

.013 

























78 


Technologic Papers of the Bureau of Standards 


Fig. 25 is a curve showing the efficiencies of corrosion as a func¬ 
tion of current density. On comparing the results of these tests 
with those previously described, it is seen that while an increase of 
voltage from 4 to 15 volts in the case of the 2-inch tubes caused 
an increase in efficiency of corrosion from 1 per cent or a little 
more to about 5 per cent, an increase of voltage from 15 volts to 
50 volts on the 6 by 8 inch cylinders caused an increase in the 
efficiency of corrosion from 2 or 3 per cent to about 40 per cent. 




EFFECT OF CHANGE OF CURRENT 

DENSITY ON EFFICIENCY OF CORROSION. 

























0 




0 







0 

0 








Persq.ln. 0 
Per cm.* 


2 

0.31 


4 

0.62 


6 

0.93 


1.24 

MILLIAMPERES 

Fig. 25 


10 

1.55 


14 

2.17 


16 

2.48 


The comparison of these results, together with the fact that where 
the high efficiencies of corrosion prevailed there was always high 
temperature, led to other tests which were designed to show the 
effects of temperature on the efficiency of corrosion. 

For the purpose of carrying out the temperature tests a number 
of cylindrical specimens 4 inches in diameter by 4 y 2 inches long 
were made up of a .1:2 mortar consisting of quartz sand and Old 
Dominion cement mixed with distilled water, the sand having 
been washed with tap water before using. A one-half inch round 
















Electrolysis in Concrete 


79 


iron electrode was embedded to a depth of 4 inches in the axis of 
each cylinder. Before embedding the iron electrodes they were 
filed to remove all scale and rust and bare copper-wire leads 
soldered to them. They were then carefully weighed, and the 
exposed portion well coated with paint to prevent natural corro¬ 
sion. When the electrodes were placed in the mortar a piece of 
glass tubing 1 inch in length and having an internal diameter of 
about seven-sixteenths inch was placed around the electrode, the 
lower end of the piece of tubing being embedded in the mortar 



Fig. 26 


to a depth of one-fourth inch. The object of this was to prevent 
leakage of current from the electrode above the mortar if the top 
of the specimen became wet while under test. After being removed 
from the molds, the specimens were allowed to set in a damp closet 
two weeks before testing. 

In order to test the specimens, they were inclosed in metal ves¬ 
sels with wooden tops which could be screwed down tight to pre¬ 
vent the rapid evaporation of water, and placed in an electrically 
heated bath of transformer oil. To obtain a fair average result 
for each value of the temperature and current density at the anode 
69133°—14-6 




























80 Technologic Papers of the Bureau of Standards 

surface, the specimens were tested in sets of four, the four speci¬ 
mens being connected in series, so that the current density might 
be the same in each. Distilled water served as the electrolyte and 
the metal vessel answered for a cathode. 

The first series of tests was carried out, using varying current 
density and constant temperature. The object of this test was 
to ascertain whether or not any variation in efficiency of corrosion 
might be directly due to a change in the current density over the 
surface of the electrode. The only temperature which could be 
relied on for constancy with all values of I 2 R in the specimen was 
boiling temperature, which, for the electrolyte, was a trifle more 
than ioo° C. Seven different current densities were used, the 
current density for each set of specimens being kept constant 
throughout the test. The results obtained are tabulated in 
Table 13, while the curve of Fig. 26 shows the efficiency of corro¬ 
sion plotted as a function of current density. 

TABLE 13 

Corrosion tests at 100° C with various current densities 


Specimen 

number. 

Time of 
test 

Total 

current 

Current 

density 

Ampere- 

hours 

Loss by 
corrosion 

Efficiency 

of 

corrosion 

Average 

efficiency 

of 

corrosion 

105. 

Hours 

148.5 

Amperes 

0.010 

M. A. 
CM2 

0. 25 

1.48 

Grams 

0.586 

Per cent 

37.8 

Per cent 

105A. 

148.5 

.010 

.25 

1.48 

.653 

42.1 


115. 

148.5 

.010 

.25 

1.48 

.626 

40.3 


Ill. 

148.5 

.010 

.25 

1.48 

.657 

42.3 

40.6 

100 . 

49.0 

.030 

.78 

1.47 

.714 

46.3 


104. 

49.0 

.030 

.78 

1.47 

.583 

38.0 


103. 

49.0 

.030 

.78 

1.47 

.654 

42.4 


102 . 

49.0 

.030 

.78 

1.47 

.743 

48.2 

43.7 

83. 

24.0 

.072 

2.0 

1.728 

.780 

43.3 


80. 

24.0 

.072 

2.0 

1. 728 

.727 

40.0 


84. 

24.0 

.072 

2.0 

1. 728 

.796 

44.2 


97. 

24.0 

.072 

2.0 

1. 728 

.861 

47.8 

43.8 

85. 

12.6 

.120 

3.5 

1.51 

.760 

48.4 


82. 

12.6 

.120 

3.3 

1. 51 

.724 

46. 1 


79. 

12.6 

.120 

3.4 

1. 51 

.820 

52.2 


75. 

12.6 

.120 

3.4 

1.51 

.788 

50.2 

49.2 

96. 

6 . 75 

.200 

5.12 

1.35 

.655 

46.3 


86 . 

6 . 75 

.200 

5.55 

1. 35 

.679 

48.1 


94. 

6.75 

.200 

5. 40 

1.35 

.715 

50.7 


87. 

6.75 

.200 

5.40 

1. 35 

.711 

50.5 

48.9 
































Electrolysis in Concrete 
TABLE 13 —Continued 


81 


Specimen 

number 

Time of 
test 

Total 

current 

Current 

density 

Ampere- 

hours 

Loss by 
corrosion 

Efficiency 

of 

corrosion 

Average 

efficiency 

of 

corrosion 

76. 

Hours 

7.0 

Amperes 

.265 

M.A. 

CM2 

7.3 

1.85 

Grams 

.786 

Per cent 

40.7 

Per cent 

74. 

7.0 

.265 

7.7 

1.85 

.886 

45.9 


77. 

7.0 

.265 

7.3 

1.85 

.831 

43.0 


92. 

7.0 

.265 

7.3 

1.85 

.860 

44.5 

43.5 

91. 

3.66 

.37 

9.7 

1. 35 

.643 

45.6 


88 . 

4.0 

.37 

10.6 

1. 48 

.805 

52.2 


89. 

4.0 

.37 

10.3 

1. 48 

.742 

48.1 


73. 

4.0 

.37 

10.3 

1.48 

.645 

41.8 


95. 

6.5 

.35 

10.3 

2.27 

1.106 

46.6 


93. 

7. 25 

.35 

10.3 

2. 53 

1.156 

43.7 

46.3 


It is seen that increasing the current density in the ratio of i to 
40 causes no material change in the efficiency of corrosion. For a 
given current density there are variations in the efficiencies of 
corrosion between individual specimens, but these variations may 
be attributed to variations in the concentrations of the dissolved 
substances of the electrolyte. A slight variation in the concen¬ 
tration of one of the solvents could easily cause a marked change 
in the efficiency of corrosion. This is especially true at the boiling 
point, because at that temperature calcium hydroxide is but 
about one-half as soluble as at room temperatures and its passivat¬ 
ing action would therefore be greatly reduced, giving any dis¬ 
solved salts of marked corrosion tendencies a much greater oppor¬ 
tunity to act in proportion to their concentrations. 

A second series of tests, the purpose of which was to show the 
effect of variation of temperature on the efficiency of corrosion, 
was conducted in a manner similar to that of the preceding series 
of tests. The range of temperature was from 3 0 to ioo° C, the 
temperature of the electrolyte being the one measured and 
recorded. In order that the heating effect of the current on the 
interior of the specimen might be nearly the same at all tempera¬ 
tures the current was kept constant and equal to 0.030 ampere 
through the four specimens of each set in series. The total average 

























EFFICIENCY OF CORROSION 


82 Technologic Papers of the Bureau of Standards 

voltage required for this was about 26 volts. The power expended 
in all four specimens was therefore 0.78 watt. Dividing this by 
4 x 4.189 gives 0.047 calorie of heat liberated in each specimen 
per second. Since heat was being constantly lost from the speci¬ 



men through evaporation of water, such a rate of heat liberation, 
distributed as it was between positive and negative electrodes, 
could not result in a material increase of the temperature of the 
interior of the specimen over that of the electrolyte. If such an 



























Electrolysis in Concrete 83 

increase took place, however, it would only mean that the curve 
showing the efficiency of corrosion as a function of temperature 
would be displaced a certain amount toward the right if the tem¬ 
perature at the surface of the electrode were known and plotted 
in place of the temperature of the electrolyte. The shape of the 
curve would not be changed. The condensed data of the test are 
given in Table 14. Fig. 27 shows a plot of efficiency of corrosion 
as a function of temperature, the temperature of the electrolyte 
being the one used, as mentioned above. 

TABLE 14 

Efficiencies Of Corrosion 


Specimen 

number 

Time of 
test 

Ampere- 

hours 

Loss by 
corrosion 

Temperature 

of 

electrolyte 

Efficiency 

of 

corrosion 

Average 
efficiency 
of corrosion 

142. 

Hours 

51.5 

1.54 

Grams 

0.026 

°C 

3.0 

Per cent 

1.60 

Per cent 

150. 

51.5 

1.54 

.037 

3.0 

2.31 


146 . 

51.5 

1.54 

.017 

3.0 

1.06 


141. 

51.5 

1.54 

.012 

3.0 

.75 

1.43 

99 . 

48.5 

1.45 

.069 

24.8 

4.54 

108. 

48.5 

1.45 

.044 

24.8 

2.90 


110 . 

48.5 

1.45 

.068 

24.8 

4.47 


113.... 

48.5 

1.45 

.053 

24.8 

3.50 

3.85 

109. 

47.8 

1.43 

.048 

31.0 

3.20 


107. 

47.8 

1.43 

.051 

31.0 

3.40 


116. 

47.8 

1.43 

.041 

31.0 

2.73 


106. 

47.8 

1.43 

.039 

31.0 

2.60 

2.98 

132 . 

48.2 

1.45 

.038 

39.5 

2.51 


114 . 

48.2 

1.45 

.042 

39.5 

2.76 


101 . 

48.2 

1.45 

.054 

39.5 

3.57 


112 . 

48.2 

1.45 

.046 

39.5 

3.04 

2.97 

132 . 

48.0 

1.44 

.031 

49.3 

2.06 


122 . 

48.0 

1.44 

.058 

49.3 

3.86 

• 

137. 

48.0 

1.44 

.038 

49.3 

2.53 


139. 

48.0 

1.44 

.041 

49.3 

2.73 

2.79 

144 . 

48.0 

1.44 

.206 

54.5 

13.70 


135. 

48.0 

1.44 

.102 

54.5 , 

6.80 


143 . 

48.0 

1.44 

.285 

54.5 

18.90 


136 . 

48.0 

1.44 

.174 

54.5 

11.50 

12.72 

124. 

48.0 

1.44 

.103 

59.9 

6.86 


121 . 

48.0 

1.44 

.138 

59.9 

9.20 


123. 

48.0 

1.44 

.218 

59.9 

14.53 


119. 

48.0 

1.44 

.102 

59.9 

6.80 

9.35 

125. 

48.3 

1.45 

.384 

70.0 

25.40 


121 .. 

48.3 

1.45 

.343 

70.0 

22.70 


128. 

48.3 

1.45 

.375 

70.0 

24.80 










































8 4 


Technologic Papers of the Bureau of Standards 
TABLE 1 A —Continued 


Specimen 

number 

Time of 
test 

Ampere- 

hours 

Loss by 
corrosion 

Temperature 

of 

electrolyte 

Efficiency 

of 

corrosion 

Average 
efficiency 
of corrosion 


Hours 


Grams 

°C 

Per cent 

Per cent 

118. 

48.3 

1.45 

.322 

70.0 

21.30 

23.55 

140. 

48.0 

1.44 

.692 

79.8 

46.10 


126. 

48.0 

1.44 

.479 

79.8 

32.00 


129. 

48.0 

1.44 

.702 

79.8 

46.80 

41.63 

130. 

48.0 

1.44 

.740 

89.5 

49.30 


134. 

48.0 

1.44 

.733 

89.5 

48.80 


133. 

48.0 

1.44 

.763 

89.5 

50.80 

49.63 

102 . 

49.0 

1.47 

.743 

100.0 

48.30 


103. 

49.0 

1.47 

.654 

100.0 

42.50 


104. 

49.0 

1.47 

.583 

100.0 

38.00 


100 . 

49.0 

1.47 

.714 

100.0 

46.50 

43.83 


The most prominent characteristic of the curve of Fig. 27 is the 
sharp bend upward which occurs in the neighborhood of the tem¬ 
perature of 50°. Below 50° the efficiency of corrosion is very 
small. Since current density has been shown to have no direct 
effect on efficiency of corrosion, the great difference in efficiency of 
corrosion between high and low voltage specimens must therefore 
be attributed to the heating effect of the current. If the heating 
effect of the current is sufficient to raise the internal temperature 
of the specimens to 50° C or more, active corrosion occurs. Below 
50° the iron remains passive, or nearly so. This has been found 
to be strictly true, however, only for normal concrete specimens to 
which no foreign ingredient of marked corrosive tendencies has 
been added, as will presently appear. 

(c) CORROSION OF IRON IN CONCRETE CONTAINING FOREIGN INGREDIENTS 

In building concrete structures it is not uncommon to add cer¬ 
tain ingredients to the mortar in mixing. One of these ingredients 
is sodium chloride, and in adding it the purpose is to lower the 
freezing point of the mixture while it is setting in cold weather. 
Calcium chloride is also used for the same purpose. Another ingre¬ 
dient commonly added to mortar is hydrated lime, the function of 
which is to reduce the percentage of voids in the concrete and thus 
render it more than ordinarily impermeable to water. A large 
number of proprietary compounds are also used with the same 






















85 


Electrolysis in Concrete 

object in view. These consist of powders, pastes, and liquids, and 
are usually added in a way calculated to affect their thorough and 
uniform distribution throughout the mass. The effect of these 
additions upon the efficiency of corrosion and other electrical prop¬ 
erties of concrete has not heretofore been investigated. A number 
of specimens were*therefore made up and tested, using as many of 
these ingredients as were at hand when the tests were instituted. 

(d) EFFECT OF WATERPROOFING COMPOUNDS 

The specimens used were of standard type, 1:2^14 concrete, 
made up in the way described at the beginning of this paper, with 
the exception that the integral compounds were included in 
the mixture. 

These were added to the cement and did not replace any of it. 
Table 15 contains the condensed data of these tests as far as they 
have been carried out to date. All of the specimens were connected 
up with the embedded electrode anode, the electrical connections 
being the same as shown in Fig. 2. Tap water was used for elec¬ 
trolyte unless otherwise designated in the table. 


TABLE 15 

Effect of Addition Integral Compounds to Concrete upon the Efficiency of Corrosion 


86 


Technologic Papers of the Bureau of Standards 


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88 Technologic Papers of the Bureau of Standards 

The addition of integrals to specimens 105 to 125, inclusive, did 
not result in a very material increase in corrosion in any case if 
specimen 111 is excepted. As mentioned in the first part of this 
paper, this specimen seems to have been abnormal in respect to its 
resistance and hence the results obtained on it should perhaps not 
be considered as representing what would happen in any consider¬ 
able number of cases if an addition of the character designated 
under specimen 111 were made to concrete. All but one of the 
other specimens of this number were corroded very badly. But 
one specimen gave evidence of no corrosion at all, which is a small 
percentage of the whole number in comparison with the percentage 
of those showing no corrosion which is found in Table 2. 

(e) EFFECT OF SALT AND CALCIUM CHLORIDE 

The effect of sodium chloride and calcium chloride proved to be 
in every way as remarkable as indicated by the work of Burgess. 
The addition of 0.02 per cent of CaCl 2 to the cement resulted in a 
very marked increase in the efficiency of corrosion. Below that 
percentage the addition of chlorine in the form of CaCl 2 did not 
seem to have an appreciable effect. One-third of 1 per cent of 
sodium chloride was found to be sufficient to destroy passivity of the 
iron almost entirely. Such a result might have been anticipated 
from the work of Hayden on the electrolytic corrosion of iron by 
direct current 26 in which it was found that the addition of am¬ 
monium chloride to a potassium bichromate solution (to the 
amount of 4 per cent of the potassium bichromate) destroyed the 
passivity of iron when made anode in the solution. With potas¬ 
sium nitrate solution the addition of ammonium chloride to the 
amount of 2 per cent of the potassium nitrate was required to de¬ 
stroy the passivity of the iron. The same work also shows the 
addition of sulphates to be much less destructive than chlorides to 
the passivity of iron anodes in solutions which normally produce 
passivity of iron. Specimens 126 and 127 had no salt added in 
making, but were tested in 3 per cent NaCl solution. 

It thus appears that great care should be exercised in selecting 
an ingredient to add to reinforced concrete for any purpose what- 


26 Hayden: Electrolytic Corrosion of Iron by Direct Current, J. Franklin Inst., 172, p. 395 . 



Electrolysis in Concrete 89 

soever, provided there is any likelihood that the structure will later 
be subjected to the action of electric currents. In such cases the 
addition of chlorine should be avoided entirely, and before using 
it an integral waterproofing should be carefully examined for the 
presence of any soluble salt having a marked tendency to increase 
corrosion of the iron. 

16. ELECTROLYTIC CLEANING OF RUSTED IRON 

In cleaning a specimen of corroded iron preparatory to weighing 
great care must be exercised in order to insure the removal of all 
corroded iron and at the same time not remove any of the pure 
metal. Numerous mechanical methods have often been employed, 
but their use often leads to serious errors. In the course of the 
present investigation it was early recognized that such methods 
could not be relied upon, and after considerable experimenting they 
were abandoned. 

Electrolytic methods were then developed for cleaning corroded 
wrought iron and cast iron which have proven entirely satisfactory. 
The first attempt to clean wrought iron of rust electrolytically was 
made by connecting it up as cathode in a 2.5 per cent H 2 S 0 4 solu¬ 
tion, using iron for the anode. The rusted iron was cleaned, but 
iron apparently dissolved from the anode and plated out at the 
cathode, causing an increase of weight which was too great to be 
neglected. The fact that the iron plated out at the cathode was 
ascertained by running a clean check specimen in parallel with and 
close to a rusted specimen and also by running a clean specimen as 
cathode with no rusted specimen accompanying it. Increase of 
weight occurred with the check specimens in both cases and seemed 
to be proportional to the time provided the current was constant. 
Pieces of one-fourth-inch round iron rod 2 T / 2 inches long, weighing 
about 15 g, were used as check specimens. The increase in 
weight of the check specimen in one case was 0.016 g after two 
hours with 1 ampere of current flowing. This was the greatest 
increase of weight noted in any case, but several other check speci¬ 
mens were run for one-half hour, one hour, and one and three- 
fourths hours, and increases in weight of 0.004 to 0.012 g occurred. 


90 Technologic Papers of the Bureau of Standards 

The solution of the problem thus seemed to depend upon finding 
a material for the anode which would be noncorrodable by 
electrolysis in a dilute solution of sulphuric acid. With this in 
mind a piece of magnetite ore (Fe 3 0 4 ) was tried in the same way 
as the iron, anode. Contact was made with the magnetite above 
the solution with mercury-solder amalgam, care being taken 
to keep the amalgam out of the electrolyte. The resistance of 
the cell was considerably increased over that with the iron anode, 
but no difficulty was encountered in making the current density 
at the cathode great enough for rapid action. A number of rusted 
specimens were cleaned with check specimens beside them and 
several check specimens were run for periods varying from one- 
half hour to seven or eight hours. In io or more trials there was 
no change of weight that could not be attributed to errors in 
weighing. The greatest change noted was 0.002 g and the 
most of them were 0.001 g or less. The magnetite anode lost 
some weight during the progress of the tests, which probably 
was due to impurities in it that were attacked by the acid. 
Exposure to the action of the acid for a number of days resulted in 
disintegration of the magnetite. The cleaning action was all 
that could be desired, however, the iron being left perfectly free 
from rust. 

The magnetite anode in the acid seemed to work perfectly, but 
the difficulty of obtaining an anode of this type of very great 
size led to the use of lead in place of magnetite. The results 
of the first tests with a lead anode were not very satisfactory. 
The iron was cleaned of rust but was blackened. Continued use 
of the same lead anode, however, seemed to give rise to a passive 
condition of the lead which gave very good results as far as cleaning 
was concerned. The blackening of the iron while being cleaned 
ceased entirely and for a period of two hours in a fresh solution 
of acid check specimens gave no sign of an appreciable change in 
weight. The passive condition of the lead doubtless, came about 
by the formation of a layer of difficultly soluble lead sulphate 
on its surface during the first hours that the current was passed 
from it. It was found necessary, however, to change the solution 
periodically. After about four hours of current flow lead would 


Electrolysis in Concrete 91 

begin to plate out and blacken the cathode, causing a change in 
weight. This rule held for a cell containing 1000 cc of solution 
and a lead anode surface of about 70 cm 2 . The current used was 
3 amperes or a little more. When the precautions of running the 
lead as anode until the passive condition was reached and changing 
the solution often enough were observed, however, the cleaning 
action was perfect and the change in weight of the cleaned iron 
negligible. 

It was found that in all cases where wrought iron was cleaned 
in acid by the electrolytic method the current flow must take 
place over the entire surface qf the iron. Neglect of this important 
point resulted in action by the acid. In order to ascertain what 
current density was necessary to completely protect the iron from 
corrosion by the acid while the cleaning process was going on a 
number of tests were carried out using various current densities. 
It was found that for different specimens of wrought iron the 
current density necessary for protection varied a good deal. In no 
case, however, did the specimens lose weight when the current 
was equal to or in excess of 0.0003 ampere per square centimeter, 
and it was therefore concluded that a current density of that 
value would be a safe one to assume for the purpose. 

An attempt to clean rusted cast iron by this method resulted 
in a total failure. The iron lost weight very rapidly even when 
the current density was very high. With a current density of 
0.01 ampere per cm 2 a specimen of clean cast iron lost 3.82 g 
in six hours. Continuing the specimen in circuit longer resulted in 
a plating out of lead at the cathode. Smaller current densities 
permitted much greater losses than the above. A trial was 
then made with a 1 per cent KOH solution (ordinary lye), using a 
piece of cast iron for the anode. A run on a check specimen of 
clean iron weighing 292 g, lasting 24 hours, with a current density 
of about 0.0003 ampere per cm 2 , resulted in a gain in the weight of 
the cathode of 0.02 g. Rusted cast iron was then tried and 
the cleaning action was found to be very good. A black deposit 
was left on the surface of the iron but it washed off quite readily. 
The iron was blackened slightly but was otherwise in good condi¬ 
tion. For small pieces of rusted wrought iron the method using 


92 Technologic Papers of the Bureau of Standards 

the lead anode is perhaps best and most convenient, while for 
large pieces of either cast or wrought iron the latter method is to be 
preferred. The latter method is also safest when close attention 
can not be given the cell while in action. If the current is stopped 
no corrosive action can take place in the latter case while in the 
former the acid attacks the iron. 

The cleaning action at the cathode in the acid solution seems 
to be due to the liberation on the surface of the iron of hydrogen. 
The liberation seems to occur on the surface of the iron rather 
than on the rust, and the resulting sudden expansion probably 
pries or knocks the rust particles loose while at the same time 
the iron itself is protected against corrosion. 

17. LABORATORY EXPERIMENTS WITH PROPOSED METHODS FOR 
MINIMIZING ELECTROLYSIS IN REINFORCED CONCRETE 

A number of methods have been proposed by various investi¬ 
gators for preventing or reducing damage in reinforced concrete 
by electrolysis. Little has been known as to the efficacy of these 
proposed remedies, however, and in order to throw further light 
on the questions regarding their practical value a number of labo¬ 
ratory experiments were instituted. These methods are, in gen¬ 
eral, only applicable to structures which are in process of erection. 

(a) REDUCING THE EFFICIENCY OF CORROSION OF THE IRON BY CHEMICAL 

MEANS 

Up to the date of this writing the attempts toward reducing the 
efficiency of corrosion by chemical means have met with very 
indifferent success. In an endeavor to contrive some means for 
reducing the efficiency of corrosion of iron when made anode in 
concrete a number of substances known to retard the natural 
corrosion of iron in their aqueous solutions were tried out. The 
names of the materials used were taken from the published work 
of Heyn and Bauer 27 and are indicated in Table 16, which gives 
the condensed data of the test. The type of specimen used for 
the test was the same as that described in connection with Table 
ii and illustrated in Fig. 24. The specimens were of 1: 2 mortar, 
made up of Old Dominion cement, quartz, sand, and distilled 


S7 Heyn and Bauer: Mitteillungen K’gl’n Materialprufungsamt, p. 45, 1908. 



Electrolysis in Concrete 


93 


water. In order to insure the uniform distribution of the chemi¬ 
cals throughout the mass they were dissolved in the water used 
in making the mortar. They were used in varying concentra¬ 
tions, and the specimens of a set containing a single chemical were 
connected in series while under test in order to have the same 
current density in each one as far as practicable. Eight speci¬ 
mens constituted a set and were connected to the 115-volt cir¬ 
cuit, thus making the drop across each specimen about 14 volts. 
Several specimens to which no additions had been made were also 
tested. Distilled water served as the electrolyte. The current 
density at the surface of the electrode varied from approximately 
20 milliamperes per square inch at the beginning of the test to 
about 0.8 of a milliampere at the end. After the specimens had 
been in circuit a sufficient length of time to give reliable results, 
they were removed and the loss of iron by electrolysis deter¬ 
mined. The resulting efficiencies of corrosion are seen to be 
extremely small in all cases, while the differences between those 
obtained with the chemicals added and those without any added 
are not of a magnitude which would suggest their use in practice 
as preventives of electrolytic damage. 

TABLE 16 

Efficiency of Corrosion in Mortar with Various Chemicals Added 


Specimen 

number 

Substance used 

Per cent 
of sub¬ 
stance by 
weight of 
cement 

Per cent 
solute in 
gaging 
water 

Concentra¬ 
tion in 
block in 
mols. per 
liter 

Ampere- 

hours 

Loss of 
iron by 
corrosion 

Effi¬ 
ciency of 
corrosion 
(per 
cent) 

133 ... . 





2.46 

Gram 

0.012 

0.47 

134. 

Chromium trioxide.... 

1.8 

3.6 

0.0955 

2.46 

.000 

.00 

135 . 

.do. 

.18 

.36 

.00955 

2.46 

.013 

.51 

136. 


.09 

.18 

.00478 

2.46 

.012 

.47 

137. 


.0018 

.036 

.000955 

2.46 

.017 

.66 

138 ... 


.009 

.018 

.000478 

2.46 

.005 

.20 

139. 


.0018 

.0036 

.0000955 

2.46 

.013 

.51 

140. 


.00018 

.00036 

.00000955 

2.46 

.002 

.08 

141. 

Potassium dichromate. 

1.72 

3.44 

.0351 

2.22 

.005 

.22 

142. 


.172 

.344 

.00351 

2.22 

.018 

.78 

143. 


.086 

.172 

.00176 

2.22 

.008 

.35 

144 


.0172 

.0344 

. 000351 

2.22 

.002 

.09 

145. 


.0086 

.0172 

.000176 

2.22 

.004 

.17 

























94 Technologic Papers of the Bureau of Standards 


TABLE 16—Continued 


Specimen 

number 

Substance used 

Per cent 
of sub¬ 
stance by 
weight of 
cement 

Per cent 
solution in 
gaging 
water 

Concentra¬ 
tion in 
block in 
mols. per 
liter 

Ampere- 

hours 

Loss of 
iron by 
corrosion 

Effi¬ 
ciency of 
corrosion 
(per 
cent) 







Gram 


146. 

Potassium dichromate 

.00172 

.00344 

.0000351 

2.22 

.035 

1.51 

147. 


.000172 

.000344 

.00000351 

2.22 

.030 

1.30 

148. 

Potassium chromate... 

1.785 

3.57 

.0546 

2.22 

.034 

1.47 

149. 

.do. 

.1785 

.357 

. 00546 

4.51 

.030 

.65 

150. 


. 01785 

.0357 

.000546 

4.51 

.057 

1.21 

151. 


.00895 

.0179 

.000273 

4.51 

.029 

.63 

152. 

.do. 

.00445 

.0089 

. 000137 

4.51 

.048 

1.04 

153. 


.001785 

.00357 

.0000546 

4.51 

.029 

.63 

154. 


. 0001785 

.000357 

. 00000546 

4.51 

.017 

.37 

155. 

.do. 




4.51 

.014 

.30 

156. 

Potassium iodate. 

1.785 

3.57 

.0496 

4.51 

.003 

.00 

157. 


.1785 

.357 

.00496 

3.80 

.015 

.37 

158. 


.0895 

.179 

.00248 

3.80 

.013 

.32 

159. 

.do. 

. 01785 

.0357 

.000496 

3.80 

.052 

1.30 

160. 


.00895 

.0179 

. 000248 

3.80 

.018 

.45 

161. 


. 001785 

.00357 

.0000496 

3.80 

.021 

.52 

162. 

.do. 

.0001795 

.000357 

.00000496 

3.80 

.182 

4.55 

163. 

Potassium bromate.... 

1.7850 

3.57 

.0656 

3.80 

.152 

3.80 

164. 


.1785 

.357 

.00654 

3.80 

.023 

.57 

165. 

.do. 

.0895 

.179 

.00329 

2.30 

.022 

.91 

166. 

.do. 

.01785 

.0357 

.000651 

2.30 

.031 

1.30 

167. 


.00895 

.0179 

. 000327 

2.30 

.006 

.25 

168. 


.001785 

.00357 

.0000654 

2.30 

.030 

1.25 

169. 

.do . 

.0001785 

.000357 

.00000649 

2.30 

.022 

.91 

170. 

.do. 




2.30 

.041 

1.70 

171. 

Potassium permanga¬ 

1.785 

3.57 

.0670 

2.30 

.048 

2.00 


nate 







172. 

.do. 

.1785 

.357 

.00675 

2.30 

.027 

1.12 

l 


It is well known that the presence of sulphates in even com¬ 
paratively small amounts tends to destroy the passive state which 
iron generally assumes in strongly alkaline solutions, and, accord¬ 
ingly, a trial was made with barium hydrate added to the 
cement in the form of a fine powder. It was believed that by 
precipitating the S0 4 ions as practically insoluble barium sulphate, 
leaving the cement comparatively free from S0 4 , the extreme 
alkalinity of the solution in the pores of saturated concrete would 
then allow the current to pass from the iron to the concrete with 
little or no corrosion of the iron. That is, the iron anode would be¬ 
come passive as it does in highly concentrated alkaline solutions. 












































95 


Electrolysis in Concrete 

The tests were carried out on 2-inch cubes of 1: 2 mortar made up 
in the same way as the cubes described in connection with Table 11. 
The tests were also conducted in the same manner. The only 
difference between the two sets of tests lay in the addition of the 
barium hydrate, which was made by percentage of weight of the 
cement. A quantity more than chemically equivalent to the S 0 4 
present was added in every case. Condensed data are given in 
Table 17. A column showing the efficiencies of corrosion obtained 
with the same cements with no Ba(OH) 2 added is also given to 
aid comparison. The S 0 4 was precipitated as BaS 0 4 and, as was 
to be expected, with the exception of the trial with the ore cement, 
the treated cements “flashed,” or set very quickly when mixed 
with water after the manner of unplastered cement. The ore 
cement did not flash, and it was thought that by mixing Ba(OH) 2 
with this slow-setting cement that a practicable application 
might be made of the scheme. 


TABLE 17 

Effect of Ba(OH) 3 on Efficiency of Corrosion 


Specimen number 

Ampere- 

hours 

Ampere- 
hour 
density 
per 
sq. in. 

Anode 

toss 

Theo¬ 

retical 

loss 

Efficiency 
of cor¬ 
rosion 

Hours to 
cracking 

Added 

Ba(OH)j 

Efficiency 
of cor¬ 
rosion, 
same ce¬ 
ment, no 
addition 




Grams 

Grams 

Per cent 


Per cent 

Per cent 

216. 

1.35 

1.06 

0.068 

1.41 

4.9 

75 

5 

1.85 

217. 

1.22 

.96 

.065 

1.27 

5.1 

75 

5 

1.97 

218 

0 

0 

.003 

0 



5 


219. 

1.72 

1.35 

.025 

1.79 

1.4 

No cracks. 

10 


220 . 

1 .77 

1 40 

.036 

1.85 

1.9 

...do. 

10 


221 

0 

0 

.005 

0 



10 


222 . 

1.76 

1.40 

.060 

1.83 

3.2 

47 

10 

15.0 

223. 

2.20 

1.76 

.038 

2.30 

1.6 

23 

10 

9.7 

224 

0 

0 

.005 

0 



10 












An examination of the results presented in Table 17, however, 
does not reveal any evidence from which we can conclude that 
the addition of barium hydroxid is of any material value in reduc¬ 
ing the efficiency of corrosion. In the case of the iron-ore cement 
there appears to have been a decrease in the corrosion, but in- the 
case of other cements the reverse is the case. 

69133°—14 - 7 
































96 Technologic Papers of the Bureau of Standards 

It should perhaps be noted in this connection that the barium 
hydrate added to the cement would have no effect on the activity 
of any soluble chlorides that might be present. 

Under ordinary conditions and at usual temperatures the 
efficiency of corrosion of iron in normal concrete is very low; 
and in the light of the above results it seems that efforts along the 
line suggested under heading (a) might most profitably be directed 
toward keeping it low by preventing the addition to the concrete 
of any acid radical of marked corrosive tendencies in a form which 
is readily dissolved and ionized. The wisdom of such a precaution 
is indicated in the section dealing with electrolytic corrosion of 
iron in concrete and should be taken, not only with reinforced con¬ 
crete in the process of making, but at every stage of its existence, 
Concrete takes up a very appreciable amount of water, and when 
a salt or an acid in solution comes in contact with its surface the 
chemical may diffuse throughout the mass. The resulting damage 
by electrolysis may be as great as if the chemical had been added 
in making the concrete. Evidence of this fact is found in a com¬ 
parison of the results obtained on specimens 126 to 132, inclusive, 
in Table 15. 

(&) PAINTING OR COATING THE IRON BEFORE EMBEDDING IT IN THE CONCRETE 

Painting or otherwise treating the iron before embedding it in 
the concrete has not as yet been tried thoroughly, the tests being 
held up to await the outcome of some experiments with a large 
number of preservative paints for iron as preventives of natural 
and electrolytic corrosion in the presence of air and moisture. 
Three standard size specimens were made up for one test along 
this line, however, using three-fourths-inch round iron electrodes 
which had been dipped in melted pitch before embedding them. 
They were connected up as anode on 15 volts and left in circuit 
more than one year. The currents in two of the specimens were 
inappreciable at all times. The third carried a current which 
varied a great deal, but the highest current reading at any time 
was only 20 mil-amperes. It is evident, therefore, that the pitch 
had considerable effect in preventing current flow, but in common 
with all paints used in this manner it has the disadvantage that no 
bond forms between the concrete and iron when the concrete sets. 


97 


Electrolysis in Concrete 


This limits the application of such a method of protection to 
structures where the strength of the bond is not an important 
matter. 


(c) SPECIFIC RESISTANCE OF CONCRETE, TESTS OF INTEGRAL WATERPROOFING, 
AND SPECIFIC RESISTANCE MEASUREMENTS OF GRANITE AND LIMESTONE 


The judicious distribution about a structure of courses of 
masonry or concrete of high specific resistance offers large pos¬ 
sibilities as a contributory means at least toward minimizing 
electrolysis in reinforced concrete in those cases where electrol¬ 
ysis might be expected to occur. Investigations were accord¬ 
ingly undertaken to ascertain the specific resistance of very wet 



Fig. 28 .—Specimens used in measuring the specific resistance of concrete . 


concrete of different proportions, methods by means of which its 
specific resistance might be increased, and also the specific resist¬ 
ances of samples of the two commonly used building materials, 
granite and limestone, in both wet and dry condition. 

The measurements of the specific resistance of wet concrete were 
conducted on 4 by 4 by 12 inch bricks made up in a manner illus¬ 
trated in Fig. 28. Table 18 gives the results of the measurements, 
and also the characteristics of the concrete with regard to pro¬ 
portions. Old Dominion cement, river sand, and crushed trap 
constituted the aggregate. The' perforated sheet-iron plates shown 
embedded in the concrete in Fig. 28 were found to act as very 
satisfactory contacts for the purpose of electrical measurements. 















g 8 Technologic Papers of the Bureau of Standards 

The concrete was 9 months old when the measurements were 
made. For three months previous to the time of making the 
measurements the bricks had been immersed in water, weighings 
being made from time to time until it was evident that no more 
water was being taken up. The specimens were then removed 
from the water, allowed to drain for a few minutes, and the resist¬ 
ance between the plates measured by alternating current using the 
ammeter-voltmeter method. In making calculations the contact 
error which would be introduced by the perforated plate was 
neglected because it would be but a very few per cent of the total 
resistance of the specimen. The result given for each proportion 
is the average obtained from measurements made on five speci¬ 
mens. The results show a decrease in the specific resistance as 
the amount of sand is increased. With the addition of both sand 
and stone an increase is noted. This peculiar variation seems to 
be most plausibly explained by a consideration of the percentage 
of voids in the mass in relation to the percentage of sand and 
rock present. The sand and stone would in themselves possess 
a very high specific resistance, while voids filled with calcium 
hydroxide solution, or other electrolyte, would have a compara¬ 
tively low specific resistance. 

TABLE 18 

Specific Resistance of Concrete 28 


Proportions of concrete 

Resistance in 
ohms cm 3 

Proportions of concrete 

Resistance in 
ohms cm 3 

Neat cem. 

3500 

1:2J:4 

8000 

1:2 . 

2300 

1:3:5... 

8200 

1:4. 

2100 

1:4:7.. 

9900 


6300 



28 The specific resistance of concrete will of course vary greatly with the aggregate, method of making, 
etc., and the above values are indicative only of the order of magnitudes of specific resistances that may 
be expected. 


The one would probably counteract the other; that is, with the 
first additions of sand the increase in the percentage of voids 
filled with calcium hydroxid solution having a low specific resist¬ 
ance would more than counteract the increase of specific resistance 
due to the lengthening of the path of the current by the presence 
















99 


Electrolysis in Concrete 

of the sand grains. A continued increase in the proportion of 
sand, or sand and rock, would finally bring about an opposite 
result. 

In a search for a solution for the problem of increasing the 
specific resistance of concrete a trial was made of a number of 
integral waterproofings for concrete which are commonly sold in 
the market. These integral compounds are sold in the form of 
powders, pastes, and liquids and are designed for incorporation 
within the mass of the concrete while mixing 'the aggregate and 
their intended function is to reduce the porosity of the mass or 
otherwise render it impermeable to water. The method of 
application varies with the character of the compound; the 
procedure generally being to mix the powders with the dry cement, 
the pastes and liquids with the water used in making the concrete- 

The concrete specimens used for the tests were of the type 
shown in Fig. i. They were made of a i: 2 %: 4 mixture, with three- 
fourths inch round iron electrodes embedded in them. Each 
compound was added to the concrete in the manner prescribed 
by its manufacturer. After the specimens had been taken out 
of the moulds they were allowed to set in water or wet sand for 
8 or 10 weeks before testing. 

The concrete containing the compounds first tested was treated 
as follows: The damp specimens were placed in an oven and 
dried at a temperature of about ioo° C, until no more water was 
given off, which was shown by the constant weight of the speci¬ 
mens. The dry specimens were then immersed to about one-half 
inch from the top of the concrete in water, the arrangement 
electrolytically and otherwise being the same as that shown in 
Fig. 2. The conductance between the embedded and outer elec¬ 
trodes was measured from time to time by alternating current, 
using the ammeter-voltmeter method. The weights of the 
specimens were also obtained at the time the conductance meas¬ 
urements were made. When the weight and conductance each 
became practically constant the test was considered finished. 
The results of this test are given in Table 19, Nos. 2 to 11, inclusive, 
the value of the conductance at the end of the test being the one 
recorded. The values of the conductance and absorption given 


ioo Technologic Papers of the Bureau of Standards 

in the table for each particular integral are the averages obtained 
from four specimens. The absorption is expressed as a percent¬ 
age of the dry concrete, the water absorbed by the dry specimen 
during the test being used in the calculation. The results obtained 
on a set of specimens to which no integral had been added are also 
given to aid comparison. The untreated set is No. i in the table. 

Realizing that the test as above described might be open to 
criticism because of the temperature used in drying it was modified 
in the cases of the remaining integrals which were tested, and in 
order to ascertain what effect might have been caused by the drying 
temperature a check test in the modified form was run on a powder 
and a paste, Nos. 4 and 6 in Table 19, both of which had been tested 
before. In the modified test the specimens were weighed and their 
conductances measured while they were still saturated with the 
water in which they had been placed, after which they were placed 
in air in the laboratory where they were allowed to dry for two 
months. At the end of the period of two months they were again 
immersed in water and weight and conductance measurements 
made in the same manner as described in the preceding paragraph. 
When the measurements were finished the specimens were dried 
at ioo° C, in order to obtain the amount of absorption. The ab¬ 
sorption in this case was taken as the difference in weight between 
approximate saturation and complete dryness of the specimens 
and is expressed as a percentage of the dry concrete. The results 
of these tests are given in Table 19, Nos. 13 to 17, inclusive. 


Electrolysis in Concrete ioi 

TABLE 19 


Effect of Various Integrals on the Specific Resistance of Concrete 


Compound number 29 

Absorption in per 
cent of dry con¬ 
crete 

Conductance be¬ 
fore specimens 
were dried 

Conductance at 
end of test 


Per cent 



l 29 . 

3.3 


0.015 

2. 

2.9 


.0092 

3. 

2.9 


.0091 

4. 

3.0 


. 0110 

5. 

2.3 


.0080 

6. 

3.2 


.0045 

7. 

3.8 


.0019 

8. 

5.9 


.0070 

9 . 

4.9 


.0030 

10. 

2.2 


.0023 

11» . 

1.6 


.00004 

12. 


0.0219 

13. 


.0134 

.0089 

14. 


.0135 

.0087 

15. 


.0077 

.0062 

16. 


.0100 

.0076 

17. 


.0112 

.0065 






29 Specimens containing compounds 2 to 11 were dried at ioo° C. before testing. No. 1 gives the results 
obtained on a set of untreated specimens which had been dried at ioo° C. Specimens containing com¬ 
pounds 13 to 17 were air dried as described. No. 12 was a set of untreated specimens which had been 
air dried. 

On comparing the different results obtained it was seen that dry¬ 
ing at ioo° of specimens made up with No. 4 and No. 6 resulted in 
a decrease in the conductivity and amount of absorption in the 
case of No. 6, while No. 4 seemed to have been changed but little. 
In view of these facts no check tests were run on the other inte¬ 
grals which had been dried at ioo°, with the exception of No. 11, 
which was the only one giving results which warranted further 
investigation. In the case of No. 11 tests were instituted to 
ascertain how long and how well it would protect against elec* 
trolysis and under what conditions the change in the specific 
resistance of the concrete was brought about. 

For these electrolysis tests five specimens were used, four of 
which had served for the absorption and conductivity tests. All 
of the specimens had been dried at ioo° C, and contained 40 per 
cent of the compound by weight of the cement. The electrolysis 
tests were conducted in the usual manner, three of the specimens 
being connected with embedded iron anode on 115 volts and the 





































102 Technologic Papers of the Bureau of Standards 

remaining two cathodes on the same voltage. Tap water served 
as the electrolyte. The currents on the anode specimens were 
from 0.005 to 0.003 ampere in value and the cathode specimens 
carried currents of from .007 to 0.016 ampere. After two and 
one-half months in circuit there were no marked detrimental effects 
to be seen upon the concrete. Two of the specimens were broken 
open, one a cathode and the other an anode. There was no 
apparent corrosion on the anode iron with the exception of a 
slight ring of rust around the rod where it emerged from the con¬ 
crete. There was but slight evidence of decomposition of the 
mortar in the vicinity of the cathode. 

In order to ascertain what conditions were required for com¬ 
pound No. 11 to affect materially the specific resistance of the 
concrete a number of cylinders were made up in the usual manner 
using 20 per cent of the compound in some cases and 40 per cent 
in others. The tests on these specimens were conducted as fol¬ 
lows: Six specimens were made up and allowed to set in water 
three and one-half months. They were then measured for con¬ 
ductance in the manner described above. The results are given 
in Table 20, specimens 381 to 386. Four of the specimens were 
then dried in an oven at ioo° C, and two were dried in air in the 
laboratory for two months. When the drying was finished they 
were placed in jars and allowed to take up water until the con¬ 
ductance became constant. The results of these measurements 
are also given. Eight other specimens were then made up using 
20 per cent of the compound. When removed from the molds 
four of the specimens were placed in air to set. The others were 
placed in a damp closet. After six weeks conductance measure¬ 
ments were made with results as shown under specimens 452 to 459. 
A comparison of the results of the conductance measurements 
shows that drying at a high temperature is essential to the attain¬ 
ment of a high specific resistance by concrete treated with this 
compound. Air drying is not sufficient and it seems, therefore, 
that in practical work this compound can be regarded as of value 
in causing an increase in the specific resistance of concrete only in 
cases where the concrete can be subjected to a high temperature 
after it has set. 


Electrolysis in Concrete 

TABLE 20 


103 


Conductance of Specimens Treated with Compound No. 11 After Setting 
Three and One Half Months in Water 


Specimen 

number 


381. 

382. 

383. 

384. 

385. 

386. 


Per cent of 
compound 

Conductance 

Dried in— 3 ® 

Loss in weight 30 

Conductance 30 

40 

0.0123 

Oven. 

Per cent 

7.1 

0 

40 

.0123 

.do. 

6.4 

0.000052 

40 

.0123 

Air 2 months... 

3.3 

.004 

20 

.0106 

Oven. 

6.1 

.000052 

20 

.0106 

.do. 

6.0 

.00021 

20 

.009 

Air 2 months... 

3.2 

.005 


Specimen 

number 

Per cent 
of 

compound 

Set in air 

Conduc¬ 

tance 

Specimen 

number 

Per cent 
of 

compound 

Set in 
damp 
closet 

Conduc¬ 

tance 

452. 

20 

Weeks 

6 

0.0079 

454. 

20 

Weeks 

6 

0.0080 

453. 

20 

6 

.0079 

455. 

20 

6 

.0074 

456. . _ 

20 

6 

.0078 

457. 

20 

6 

.0075 

458. 

20 

6 

.0074 

459. 

20 

6 

.0072 


30 Conductance measurements after drying and being reimmersed. 


In making an interpretation of the results of these tests on inte¬ 
gral waterproofings the tendency of normal reinforced concrete to 
protect itself against the effect of electric currents should be con¬ 
sidered. In the section dealing with the rise of resistance of rein¬ 
forced concrete due to flow of current it is seen that when saturated 
specimens are subjected to the action of current the rise of resist¬ 
ance is sufficient within a few weeks to prevent damage unless 
the conditions of electrolysis are extremely severe. (See No. 1, 
Table 22.) Therefore, unless a waterproofing integral causes a 
decrease in the conductivity of concrete under the conditions of 
application in practice to an amount comparable with that 
observed in connection with the flow of current through normal 
reinforced concrete its use would not be justified merely on the 
ground of preventing electrolysis. That is, in order to be efficient 
in the prevention of electrolysis the addition of the waterproofing 
agents should cause a reduction in the conductivity of wet concrete 
to 1 or 2 per cent of its normal value instead of to 50 per cent, as 








































104 Technologic Papers of the Bureau of Standards 

most of them do. The reason for this is found in the fact that the 
effect of the compound on the conductivity of the concrete is only 
additive. Speaking in terms of resistance, the statement that the 
effect is additive may be made clear by the following: Suppose 
two specimens of reinforced concrete to be made up in exactly the 
same manner excepting that to one a waterproofing integral is 
added. When both are thoroughly set and saturated with water 
the resistance of the untreated specimen will probably be about 
ioo ohms, while that of the treated specimen will be, say, 200 
ohms. If both are put in circuit with embedded metal anode and 
current allowed to flow for three months or so the resistance of the 
untreated specimen will rise to about 10 000 ohms. At the same 
time the resistance of the treated specimen will be found to have 
increased to about 10 100 ohms, both specimens having been 
subjected to the same conditions of voltage, showing practically 
no advantage in favor of the latter. A comparison of the ultimate 
resistances of the specimens of Table 2 with the ultimate resist¬ 
ances of specimens 112 to 125, inclusive, of Table 15 shows the 
above numerical example to be a fair illustration of what will 
occur. From this it appears that the mere fact that the addition 
of a waterproofing agent increases the initial resistance by a 
considerable amount should not be construed as evidence of its 
value as a permanent protection against electrolysis. 

The specific resistance measurements of granite and limestone 
were conducted on a total of seven specimens, six of granite and 
one of limestone. Two kinds of granite were represented, one 
gray and the other red. In preparing the specimens for testing 
parallel faces were ground on them and the edges ground off to a 
more or less regular geometrical outline in each case. The speci¬ 
mens were then dried at a temperature of ioo° C for two weeks. 
No losses of weight were .recorded in the case of the granite because 
they were too small to be of consequence, but the limestone speci¬ 
men showed rather remarkable absorptive qualities, the 2-inch 
cube of limestone losing 13.1 g in weight in passing from approxi¬ 
mate saturation to dryness. This is about 4 per cent in weight 
and shows that the particular limestone specimen used contained 
pores to the extent of nearly 10.5 per cent of its volume. 


Electrolysis in Concrete 105 

.The electrical measurements were made with alternating cur¬ 
rent, using the ammeter-voltmeter method. Contact was made 
to the parallel faces of the specimens with mercury-solder amalgam. 
A high resistance ammeter (831 ohms, 0.050 ampere total scale 
reading) was placed in series with the specimen and the voltage 
applied in steps up to 750 volts. The voltage was measured by 
means of a voltmeter connected across the terminals of the primary 
coil of the 1:10 ratio transformer used in stepping up the voltage. 
A current of about 1 milliampere gave a perceptible deflection of 
the ammeter needle and the results given for the dry granite and 
limestone in Table 21 are calculated on the assumption that 1 
milliampere was the smallest reading that could be obtained. 

After the measurements on the dry granite and limestone were 
completed the specimens were immersed in a saturated solution of 
calcium-hydroxide and allowed to soak for two months. At the 
end of this period they were removed from the solution, the water 
which clung to the surface wiped off and the resistance measure¬ 
ments repeated while the surfaces of the specimens were still 
damp. Table 21 gives the results of the two sets of measurements, 
the specific resistances being calculated from the resistance of 
each specimen and its dimensions. 

TABLE 21 

Specific Resistance Measurements of Dry and Saturated Specimens of 
Granite and Limestone 

DRY SPECIMENS 


Specimen 

number 

Kind of stone 

Average 
area of 
specimen 

Average 

thickness 

Voltage 

applied 

Current 

Total 

resistance 

Specific 

resistance 

225. 

Gray granite. 

cm 2 

95.3 

cm 

5.8 

750 

ampere 

< 0.01 

ohms 

> 75 000 

>1 200 000 

226. 

.. .do. 

79.6 

7.6 

750 

< 

.01 

> 75 000 

>1 200 000 

227. 

.do. 

61.1 

5.8 

750 

< 

.01 

> 75 000 

>1 200 000 

228.. 

do. 

77.5 

5.5 

750 

< .01 

> 75 000 

>1 200 000 

229 ... . 

Red granite. 

35.1 

3.4 

750 

< .01 

> 75 000 

>1 200 000 

230. 

Gray granite. 

14.0 

3.3 

750 

< .01 

> 75 000 

>1 200 000 

231. 

Limestone. 

25.0 

5.0 

750 

< .01 

> 75 000 

>1 200 000 

























io6 


Technologic Papers of the Bureau of Standards 
TABLE 21 —Continued 
SATURATED SPECIMENS—SURFACES DAMP 


Specimen 

number 

Kind of stone 

Average 
area of 
specimen 

Average 

thickness 

Voltage 

applied 

Current 

Total 

resistance 

Specific 

resistance 



cm 2 

cm 


ampere 

ohms 


225. 

Gray granite 

95.3 

5.8 

600 

0.015 

39 200 

642 880 

226. 

.do. 

79.6 

7.6 

710 

.009 

77 700 

809 000 

227. 

.do. 

61.1 

5.8 

600 

.015 

39 200 

411 600 

228. 

.do. 

77.5 

5.5 

710 

.015 

46 600 

657 000 

229. 

Red granite. 

35.1 

3.4 

710 

.001 

710 000 

7 100 000 

230. 

Gray granite . ... 

14.0 

3.3 

700 

.003 

233 000 

978 600 

231. 

Limestone. 

25.0 

5.0 

250 

.019 

12 300 

61 500 


The value of the specific resistance of the water-soaked speci¬ 
mens is the most important, and a comparison of the values given 
in Table 21 with the specific resistance of saturated concrete 
already given shows that the resistance of the limestone ranges 
about six or eight times that of concrete and the resistance of 
granite is of the order of a hundred times that of concrete. The 
latter value particularly is sufficient to warrant its use in- many 
instances in the footings and foundations of buildings in order to 
reduce the tendency of electric currents to flow between them and 
the earth. 

(d) TESTS ON WATERPROOFING PAINTS AND MEMBRANES FOR CONCRETE 

In a search for an effective and durable insulating coating 
which might be applied to the surface of concrete some tests were 
made of a number of waterproofing and damp-proofing paints 
and membranes. For the purpose of testing these paints and 
membranes they were applied to concrete cylinders of the same 
description as those used in testing for the effect of integral water¬ 
proofing, with the exception that the integrals were omitted in 
mixing the aggregate. After the concrete had set thoroughly the 
cylinders were dried at ioo° C until no more water was given off 
and the application of the paint followed when the cylinders had 
cooled. 
























Electrolysis in Concrete 


107 


In applying tne paints great care was exercised to obtain con¬ 
tinuous and flawless films as far as the character of the paints 
would permit. The directions of the manufacturers were followed 
closely, and after the finishing coat had been applied the specimens 
were set aside for a period varying from four to six weeks before 
testing. In order to avoid bruising the coating on the bottom of 
the cylinder where it came in contact with the floor in handling 
the coating was there treated with a layer of melted paraffin. 



Fig. 29 


This prevented sticking, and as far as the tests were conducted it 
seemed to have no detrimental effect on the paints. Trial showed 
that there is a vast difference between painting over a paraffined 
surface and putting a layer of paraffin over dried paint. In the 
first instance the paint never dries, but in the second no sign of 
deterioration ever appeared in the 40 or more paints tested in 
the course of this work. 

The test on the paints was conducted in much the same way as 
the tests for the effect of integral waterproofings; that is, the 
dry, painted specimens were weighed, then immersed to about 




















108 Technologic Papers of the Bureau of Standards 

one-half inch from the top of the concrete in water as shown in 
Fig. 2 and the conductance between the embedded iron and the 
outer electrode measured in each case by alternating current, 
using the ammeter-voltmeter method. After 15 to 30 minutes 
immersion, according to the characteristics of the coatings, the 
specimens were again measured for conductance, then removed 
from the jars, allowed to drain two or three minutes, and weighed. 
This operation was repeated at increasing intervals during the 



Fig. 30 


next seven days, a period of time which was usually long enough 
to give definite results. If a paint showed signs of holding out 
indefinitely the cylinders which had been treated with it were put 
aside in water and the measurements continued at intervals of 
several weeks. 

For the test of each paint a set of four specimens was used and 
the average results were plotted in the form of curves showing 
increase of weight by absorption of water, and increase of con¬ 
ductance, with time. Examples of these curves are shown in Figs. 






























Electrolysis in Concrete 


109 


29, 30, and 31. Calculations were made from each set of absorp¬ 
tion curves to show the rate of absorption of water near the 
beginning of the test, the area covered by the paraffin being 
subtracted from the total submerged area in so doing because 
such a coating was found to be almost absolutely waterproof 
during the time of the test. The rate of absorption near the 
beginning of the test was taken as the true measure of the effi¬ 
ciency of the coating as a waterproofer because at any subsequent 


52.0 

<0 

CO 


^ 0.5 












AVERAGE ABSORPTION AND CONDUCTANCE CURVES 

OF 4 CONCRETE SPECIMENS PAINTED WITH 2 COATS OP 

A PRESERVATIVE PAINT, INTENDED FOR APPLICATION 

TO CONCRETE OR IRON. 































*< 

ABSORP1 

ION-HOU 

IS / 

CONDUC" 

rANCE-D/ 

b=== 

YS 


,010 


.008 


.002 


4 5 

HOURS-DAYS 

Fig. 31 


time the specimens had become more or less saturated with water 
with a consequent decrease in the rate of absorption, which was 
not due to any property of the coating. Table 22 gives the con¬ 
densed data of the specimens and the results of the tests. 
























no Technologic Papers of the Bureau of Standards 

TABLE 22 

Results of Tests on Paints for Waterproofing Concrete 


Number of paint or 
coating 

Coats 

Rate of 
absorp¬ 
tion (cc 
per sq. 
deci¬ 
meter 
per hour 

Conduc¬ 
tance at 
end of 
seven 
days 

Number of paint or 
coating 

Coats 

Rate of 
absorp¬ 
tion (cc 
per sq. 
deci¬ 
meter 
per hour 

Conduc¬ 
tance at 
end of 
seven 
days 

li. 


40.4 

0.015 

23. 

2 

3.23 

0.002400 

2 

2 

. 11 

. 000018 

24. 

2 

3.98 

. 004500 

3 

2 

.19 

.000300 

25. 

4 

3.23 

. 006500 

4 . 

2 

1.40 

. 004800 

26. 

5 

5.38 

.015000 

5 

2 

3.75 

. 005300 

27. 

2 

.75 

.007200 

6 

1 

.11 

.000050 

28. 

3 

16.20 

.014000 

7 . 

3 

.22 

.000050 

29. 

2 

1.94 

.012000 

8 . 

3 

.07 

.000300 

30. 

1 

16.10 

.016000 

9 

3 

.30 

. 000900 

31. 

3 

1.94 

.011000 

10 

2 

.27 

.001000 

32. 

2 

.06 

.000040 

11 

2 

2.58 

. 003800 

33. 

2 

.31 

.000490 

12 . 

2 

.14 

. 000600 

34. 

2 

2.69 

.007000 

13 . . 

2 

.18 

. 001500 

35. 

1 

.65 

. 002600 

14 

2 

.88 

. 005500 

36. 

2 

1.40 

.002800 

15. 

2 

.44 

.001700 

37. 

2 

5.60 

.008100 

16 

2 

.34 

.002000 

38.,. 

2 

.75 

. 000800 

17 

2 

3.34 

. 007000 

39. 

2 

.75 

.000300 

18. 

2 

.60 

. 005500 

40. 

2 

.81 

.000350 

19.,. 

2 

1.30 

.004000 

41. 

2 

.22 

. 000150 

20 . 

2 

.21 

. 000500 

42. 

2 

.11 

. 000000 

21 

2 

.13 

. 000000 

43. 

2 

.11 

.00015 

22 . 

2 

.31 

. 000580 

44. 

2 

10.80 

.0031 










i Specimens not coated. 

NOTE.—la, Conductance by direct current of untreated specimens after current flow for one month on 15 
volts=0.0046. lb. Conductance by direct current of untreated specimens after current flow for three months 
on 15 volts= 0.00028. lc. Conductance by direct current of untreated specimens after current flow for nine 
months on 15 volts=0.000093. 


The results include the average rate of absorption of water in 
cubic centimeters per square decimeter per hour near the beginning 
of the test and the average conductance of the specimens at the 
end of seven days. A comparison of these results with those 
obtained on a set of untreated specimens gives an indication of 
the efficiency of each coating as a waterproofer and an insulator. 
The most important figures in Table 22 in relation to the work 
dealt with in this paper are those of the conductance. The greater 
portion of the coatings show conductances at the end of seven 
days which are too large to allow them to be considered as insula- 






























































Ill 


Electrolysis in Concrete 

ting. There are others, however, which show very favorable 
results in comparison with untreated normal specimens after 
being three months under test on 15 volts and their use where 
occasion demands it might be desirable if a life test on them should 
indicate that their insulating power is not too short lived. Life 
tests were not run in connection with the present work, partly 
because of lack of time. 

Some tests were also run on specimens similar to the above 
treated with waterproofing membranes. These membranes con¬ 
sist of alternate applications of hot pitch, or asphalt, and fabric. 
They are designed for waterproofing against hydrostatic pressure, 
underground. In placing the membranes the concrete was first 
thoroughly swabbed with the melted compound, then a layer of 
fabric rolled on and it in turn swabbed with more of the melted 
compound. The operation was repeated until the required 
number of layers were obtained. Great care was exercised in 
breaking joints and filling all holes where leakage might possibly 
occur. The tops of the specimens did not come in contact with 
the water in testing, so were not laid over with fabric but were 
simply painted with a thick coat of the melted compound. 

The tests on the membranes were conducted in a manner 
slightly different from those on the paints. After the specimens 
were made up they were weighed, placed in a tank containing 
water 7 inches deep and connected up with the embedded iron 
anode on the 15-volt circuit. The potential was left on con¬ 
tinuously. At intervals of a month or two current readings were 
made and the specimens were removed from the tank and weighed. 
Two different brands of membranes were tested in this way, using 
from two to five layers. Four specimens constituted a set in 
each case and the results given in Table 23 are the averages of 
the several sets. The tests were continued for 14 months and 
the electrical readings are those obtained at the end of that time. 
The effectiveness of these coatings as preventives of electrolysis 
in the manner for which they are adapted is unquestionable, 
provided, of course, that the membrane is applied with sufficient 
care. 


69133°—14-8 


112 Technologic Papers of the Bureau of Standards 

A test which throws further light on the comparative values as 
insulators of the membranes mentioned above is one a description 
of which follows. The test included pitch and felt as well as 
asphalt and felt. Five alternate layers of melted compound and 
felt were laid on one side of a piece of glass 3^ inches wide by 5 
inches long, making up three specimens of this kind in the case of 


z 

o 

l 

sc 

s 

CO 


0 2 4 6 8 10 12 14 16 10 

DAYS 
Figt 32 

each product tested. The top layer of felt was thoroughly swabbed 
over with the melted compound. 

The specimens were then carefully weighed and two of each set 
immersed in water, while the other was left in air for a check. 
From time to time the specimens were weighed, those in the water 
first being removed and wiped of water clinging to their surfaces. 
This operation was continued for about two weeks. The check 
specimens showed no appreciable change in weight. Fig. 32 gives 
the results obtained on the specimens subjected to water in the 
form of curves showing increase of weight with time. Each curve 
is the average result obtained on the two specimens. 
























Electrolysis in Concrete 
TABLE 23 

Tests on Waterproofing Membranes 




Number of product 

Layers 

used 

Rate of absorp¬ 
tion of water 
(cc per square 
decimeter 
per hour) 

Conductance 
of coating 

1 . 

5 

0.0023 

0 

1 . . 

3 

0.0016 

0 

1 . 

2 

0.0012 

0 

2 . 

5 

0.0030 

0 

2 . 

3 

0.0032 

0.000001 

2 . 

2 

0.0045 

.00004 






III. POSSIBILITIES OF TROUBLE FROM ELECTROLYSIS 
IN CONCRETE STRUCTURES UNDER PRACTICAL CON¬ 
DITIONS 

As mentioned in the introduction to the present paper, reports 
have become current from time to time during the last few years 
that more or less serious trouble has occurred in concrete struc¬ 
tures as a result of electrolysis, and in some cases serious damage 
has been reported. Since the reports of such trouble have in some 
instances been made in leading technical papers by reputable engi¬ 
neers, it became imperative that a thorough investigation of the 
practical aspect of the problem be made. In connection with the 
investigations described in the preceding section, the matter has 
been studied from the practical standpoint also, in order to deter¬ 
mine, as far as possible, to what extent the conditions under which 
concrete can be injured in the laboratory may be expected to 
obtain in practice. 

18. CONDITIONS NECESSARY FOR DAMAGE TO OCCUR 

A careful study of the data presented in the preceding pages 
shows conclusively that while there are conditions under which 
reinforced concrete may be seriously injured, such conditions are 
nevertheless exceptional rather than the rule. These exceptional 
conditions occur, however, with sufficient frequency to make the 
problem one of great importance, and fortunately most of these 














114 Technologic Papers of the Bureau of Standards 

conditions are amenable to control. It has been seen that the 
most important essentials to the injury of concrete by electrolysis 
are moisture and a difference of potential between electrodes in 
contact with the mass of the concrete. At first thought it might 
appear that these two conditions are almost omnipresent, since 
perfectly dry concrete, especially below grade, is seldom if ever 
found; while, as every electrical engineer knows, there are few 
places in our cities at the present time where appreciable differ¬ 
ences of potential can not be found between any two points more 
than a few yards apart. The statement in regard to the rarity of 
dry concrete is made advisedly, since only the most minute quan¬ 
tities of moisture are necessary in order to impart to concrete a 
considerable conductivity. On the other hand, the concrete has 
to be made very wet in order to impart to it a maximum of con¬ 
ductivity, and any reduction of the moisture content below the 
saturation point causes an increase in its resistance and a conse¬ 
quent decrease in the current which will flow through the concrete 
under a given potential gradient. As indicated by data already 
presented, the resistance of ordinary air-dried concrete, while 
extremely variable, is usually of the order of about ten times that 
of wet concrete, and for this reason concrete above grade is much 
less susceptible to electrolytic damage than if so located as to be 
permanently wet. It is not to be inferred, however, that air- 
dried concrete is immune from electrolysis troubles, but rarely 
would the voltage be high enough to produce trouble; and, in gen¬ 
eral, in the absence of special conditions to be mentioned in the 
next section, electrolytic damage to concrete above grade will be 
extremely rare. 

The condition mentioned above, mat the electric current must 
flow between electrodes in contact with the concrete, should be 
emphasized. The conduction being electrolytic, the reactions 
take place only at the electrodes, and in the absence of such 
electrodes no reactions occur within the concrete. The only effect, 
therefore, would be the slow removal of the water-soluble con¬ 
stituents, and hence the effect on the concrete would not be essen¬ 
tially different from that of slow water seepage. 


Electrolysis in Concrete 115 

19. SOURCES OF STRAY CURRENTS 

If there be electrodes embedded within the concrete, as in the 
case of reinforced concrete structures, the electrode effects described 
in the foregoing section maybe expected provided the voltage is suf¬ 
ficient. The sources of potential differences in concrete structures 
may be classed under two heads, (1) those due to direct contact 
between the conductors of lighting or power circuits, and some part 
of the building and (2) those which have their origin in stray cur¬ 
rents from railways or other grounded power lines. The former may 
happen in any building containing electric wires, through defective 
insulation. It is not necessary, of course, that both sides of the 
line be grounded in the building itself, since if one side of the line 
is grounded on the building and the other grounded in some 
remote quarter of the system those portions of the building itself 
near the grounded wire will be subjected to a considerable difference 
of potential. If the wire be grounded directly on the concrete 
and not on the reinforcement, the comparatively small cross sec¬ 
tion of the path of the current near the point of contact between 
the concrete and the wire will result in most of the total drop of 
potential to ground occurring within a restricted region near the 
wire, and it is only here that any damage may be expected, and 
since the current will be small the damage, if any, will be small. 
Ultimately, of course, any current that leaks off from the wire 
would pass out into the earth through the footings and founda¬ 
tions and through pipe systems entering the building. As a rule, 
the cross section of these paths is so large in the aggregate that 
the potential gradients would not be sufficient to raise the tem¬ 
perature appreciably, and hence no appreciable damage is likely 
to occur. If the current be reversed, flowing to the building 
from outside, there would in time be some softening of the concrete 
in a thin layer under and around the steel structure terminating 
in the footing, but this would be under compression and not 
subjected to shear along the surface of contact between steel and 
concrete, so that failure here is extremely improbable. The only 
places where trouble is to be expected due to grounding of power 
wires directly on the concrete inside of a building is in the region 
close to the point of ground. 


n6 Technologic Papers of the Bureau of Standards 

If, however, the power wire be grounded directly on a portion 
of the reinforcing material, the condition will be more serious, 
and the extent of the danger will be greater if there is a large 
quantity of the reinforcing material in metallic contact with the 
electric circuit. If this comprises a large part of the total rein¬ 
forcement of the building, the condition might be serious irrespec¬ 
tive of whether the positive or negative side of the line is grounded. 
If the ground is on the positive side, the potential gradient near 
the reinforcement may become high enough to cause rapid corro¬ 
sion and consequent destruction of the reinforcing material. If, 
on the other hand, the reinforcing material be negative, there 
would develop a softened condition of the concrete near the surface 
of the iron which would practically destroy the bond, and this 
would probably be the more serious condition of the two, since 
the latter would not manifest itself by producing local cracks in 
the concrete, and might not become known until a large portion 
of the building has become weakened. However, while such a 
condition as this might occur, and if neglected become very serious, 
it is nevertheless a trouble that can be readily guarded against, 
as will be pointed out below. 

The other source of current that might possibly give rise to 
trouble under certain circumstances is the ground return of rail¬ 
ways. The current may enter a building in two different ways. 
First, if the foundations under the two opposite sides of the 
building are at different potentials, there would be a tendency for 
a certain amount of current to flow up through the foundation on 
the one side, through the walls and floors of the building and out 
through the foundation on the other side. This condition may be 
said to exist to a very small extent in practically all concrete 
buildings, but it is not one that need cause any alarm. In the 
course of numerous electrolysis surveys that we have carried out 
in various cities we have found that a potential difference exceed¬ 
ing a few volts due to stray currents between any two parts of a 
building is extremely rare, and this would almost inevitably be 
distributed over so great a distance that the potential gradient 
would not be sufficient to cause any appreciable trouble, in view 
of the experimental results set forth in the first section of this 


Electrolysis in Concrete 117 

paper, which show that under ordinary conditions comparatively 
large potential gradients are required before any material damage 
is likely to occur. 

The second way in which stray currents may enter a building is 
through water or gas pipes, lead cable sheaths, and similar struc¬ 
tures. In this case considerably larger differences of potential may 
be brought about between different portions of the building and 
between parts of the building and the earth. If the pipe systems 
come in contact only with the concrete and not with the rein¬ 
forcing material, any damage that may occur will be slight and 
will be confined chiefly to the immediate vicinity of the pipes or 
cables; but if the pipes come into metallic contact with the rein¬ 
forcing material, the latter comes to the same potential as the 
pipes and may become either anode or cathode, according to the 
condition of the pipes. Cases may arise in practice where differ¬ 
ences of potential of serious magnitude may be produced in this 
way, some instances having been brought to our attention in 
which the reinforcing material was from 5 to 15 volts above or 
below the earth. Under most conditions damage would proceed 
very slowly under such differences of potential as these, but never¬ 
theless wherever voltages of this magnitude exist it should be 
regarded as a dangerous condition and should be remedied at 
once. 

20. INCREASED DANGER DUE TO PRESENCE OF SALT 

The above statements in regard to the liability of damage under 
low or moderate differences of potential are intended to apply 
only to concrete which contains no appreciable quantities of salt. 
The data given in the preceding section show that if a small 
quantity of sodium chloride or calcium chloride be added to the 
concrete the rate of deterioration proceeds many times faster, and 
under such circumstances much lower voltages should be regarded 
as dangerous. Even a small fraction of 1 per cent of chlorine in 
concrete is capable of increasing the electrolytic corrosion of the 
iron manyfold, and if salt has been added to the concrete during 
construction, or if it comes into contact with salt water afterwards, 
much greater precautions are necessary in order to prevent damage. 


118 Technologic Papers of the Bureau of Standards 

In the course of our investigations we have examined a consid¬ 
erable number of cases in which damage to concrete structures has 
been attributed to electric currents. Some of these have been 
reinforced structures and some have been without reinforcement. 
Among these we have not found any nonreinforced structures in 
which the conditions indicated that electric currents could in 
any way be responsible for the damage. Among the reinforced 
structures which have been called to our attention there are some 
in which electrolysis has been at least a contributing cause of the 
damage. We have not, however, seen any case in which serious 
damage has occurred in which there was not also present a con¬ 
siderable quantity of salt in the concrete, either from having been 
put there during construction or from contact with salt water in 
service. This is in accord with the results of our laboratory in¬ 
vestigations, which show that under low or moderate voltages the 
rate of damage, in the absence of chlorine, is so slow as to be 
almost negligible, but that when salt is present rapid deterioration 
at both electrodes may be expected even on comparatively low 
voltage. 

21. SOME SPECIFIC CASES OF TROUBLE 

In making an examination of these cases the condition of the 
concrete was carefully noted and compared with that of specimens 
known to have been injured by electric currents in the laboratory. 
Potential measurements were made between different parts of the 
structure, and also between the structure itself and surrounding 
structures, although the latter are as a rule not important since 
the electrical resistance between different structures is usually 
unknown, and hence the voltage readings give no idea of the cur¬ 
rent flow. By comparing the potential gradients observed with 
those used in the laboratory and considering also the age of the 
structure and any special conditions which may have influenced it, 
we are enabled to judge as to whether it is possible for the damage 
to have been caused by electric currents, and this judgment is 
further confirmed by studying the character of the damage and 
noting whether it is in any way similar to the damage that can be 
caused by electrolysis. One or two specific cases may be mentioned 
here as instances. The concrete foundations of a small bridge 


Electrolysis in Concrete 


119 

across the Gowanus Canal at Hamilton Avenue, South Brooklyn, 
developed large cracks in a number of places, and the damage had 
been attributed by some to electrolysis. On the strength of the 
first reports we were inclined to attribute the trouble to electrolysis, 
since a trolley line passed over the bridge, and it seemed quite prob¬ 
able that conditions might have arisen whereby a sufficiently high 
potential gradient had been produced to corrode the reinforcing 
material and crack the concrete. On making an examination of 
the bridge, however, it was found that those portions in which 
failure had occurred did not contain any reinforcing material, and 
the cracks were not so located that they could have been caused by 
corrosion of iron, nor could there have been a weakness due to a 
cathode effect, since there were no electrodes near the cracks and 
the concrete nowhere showed evidence of softening. In short, 
there was no similarity between the damage found here and any 
of the effects which we have noted in the laboratory. Further, 
potential measurements showed that the maximum potential dif¬ 
ference to be found was 1.6 volts, while potential gradient measure¬ 
ments between points 2 feet apart near some of the cracks showed 
values ranging from 0.01 to 0.05 volts per foot. In our experi¬ 
ments at the Bureau of Standards we have impressed on wet 
concrete blocks potential gradients of about 100 volts per foot, 
continuously for a year and a half using noncorrodible electrodes, 
without producing any cracking such as observed in this bridge. 
It seems inconceivable that such small potential gradients as found 
here could have been responsible for the cracking of the unrein¬ 
forced portions of the structure, when potential gradients in the 
laboratory 2000 times greater failed to produce any damage at all, 
except such as noted in the foregoing chapters and which was 
always closely associated with the reinforcement in the concrete. 
Further, there was evidence that the foundations of the structure 
were unstable, as shown by the fact that they had moved several 
inches toward the canal since they were built. We are informed 
that somewhat similar trouble has been experienced in a number 
of buildings in this vicitiity, indicating that the earth in this locality 
does not afford a stable support for the foundations. This alone 
would seem to be capable of causing trouble of the nature that has 


120 Technologic Papers of the Bureau of Standards 

actually occurred here, whereas as just indicated the damage is not 
of a nature that has been observed to result from the passage of 
electric current. 

One other instance may be cited here because of its importance. 
Some concrete-lined railway tunnels had suffered considerable 
damage due to disintegration of the concrete and in some instances 
within a few months after the work had been completed. A num¬ 
ber of engineers had pronounced the trouble due to electrolysis, and 
the engineers of the Bureau of Standards were asked to make an 
investigation. A voltage survey throughout the tunnels was 
made, potential measurements being taken between points on the 
tunnel walls in both a vertical and horizontal direction, and in 
some cases holes were drilled in the wall and voltage measurements 
made in a direction at right angles to the surface. Some measure¬ 
ments were also made between walls on opposite sides of the tunnel, 
and in two or three cases between the tunnel wall and the rails. 
The measurements taken were classified under three heads, viz, 
those taken where the concrete was very badly disintegrated , those 
taken where there was but slight disintegration, and those taken 
where the concrete was perfectly sound. A comparison of the 
magnitudes of the voltage' showed first that there is no definite 
relationship between the magnitude of the potential gradients ob¬ 
served and the physical condition of the concrete. The average 
voltage per foot in the first group where the concrete was very 
badly damaged was o.oi 7 volt. In the second group where there 
was no damage whatever the average potential gradient was 0.027 
volt per foot. These figures do not support the view that the 
trouble is caused by stray electric currents. It should be noted 
that in a number of places measurements were obtained where the 
concrete was very wet and yet in perfect condition, and in which 
the potential gradients were of the same order as those in the first 
group, where the concrete was badly damaged. 

In taking the readings the usual method of making contact at 
points between which measurements were to be taken could not 
be used, because the high resistances at the contact points would 
absorb the major part of the total voltage. Special terminals were 
designed, consisting of brass cups 2 inches in diameter, in each of 


I 21 


Electrolysis in Concrete 

which was compressed a sponge saturated with a solution of copper 
sulphate. Inside the cup and below the sponge was a brass piston, 
which was used as the instrument terminal. When readings were 
to be taken, the cups were placed against the concrete wall at 
points between which the voltage was to be measured with the 
piston pressing the sponge firmly against the wall. This gave a 
large surface of contact and therefore a relatively low resistance. 
Even in this case, however, it was found.that the resistance of 
the contacts was still too high to permit of using a voltmeter, and 
therefore a special high sensibility portable galvanometer connected 
in series with a megohm resistance was used. Careful tests in the 
laboratory showed that the accuracy of the measurements was 
within 3 per cent, even on nearly dry concrete, and considerably 
higher when the concrete was wet. 

The fact that there is no definite relationship between the volt¬ 
ages observed and the condition of the concrete is not surprising, 
particularly in view of the low values of most of the readings. In 
our experiments at the Bureau of Standards we have subjected 
blocks of wet concrete to potential gradients varying from very 
low values up to several thousand times the average values ob¬ 
served in the tunnels mentioned above, for a period of one and one 
half years, without producing any appreciable diminution in the 
crushing strength of the main body of the concrete, and there is no 
evidence of any other action except in the immediate vicinity of 
the electrodes. We wish to emphasize the fact that in concrete, 
as in all other electrolytic conductors, all chemical reactions which 
take place as a result of the current are essentially electrode effects, 
and they do not, except by progressive action from the electrodes, 
affect the mass of the concrete. 

In the region of the cathode there is a softening of the concrete, 
but as pointed out above it begins as a thin film on the surface of 
the cathode and very slowly progresses outward. There is a sharp 
line of demarkation between the injured and uninjured area, the 
main body of the concrete being unaffected. The rate at which 
this softened region progresses outward from the electrode is so 
slow that it could not possibly give rise to the phenomena observed 
in the tunnels in question. In our experiments with normal con- 


122 Technologic Papers of the Bureau of Standards 

Crete in which we have used potential gradients up to about 5000 
times those found in these structures, we have found that the rate 
at which the softened region moves outward from the cathode is 
not over about an inch per year, and the concrete outside this very 
restricted area always remains perfectly sound. In the light of 
these experiments and considering the relatively low potential gra¬ 
dients existing in and around these concrete structures the theory 
that damage of this nature could have spread over such vast areas 
in so short a time is absolutely untenable. After a careful study 
of the conditions existing in these tunnels we were forced to the 
conclusions that electrolysis has played no appreciable part in the 
damage which has been experienced. 

22. PROCEDURE IN MAKING VOLTAGE MEASUREMENTS ON CONCRETE 
STRUCTURES 

We desire to say a word in regard to the proper method of taking 
electrical measurements that are intended to show whether or not 
a structure is being affected by stray currents. The apparatus 
which we have used successfully has already been described. It 
is not only important to read the voltages correctly, but it is 
equally important to take the measurements between the proper 
points and to properly interpret them. We have known cases 
where damage has been attributed to stray currents on the strength 
of potential measurements taken between the structure and the 
rails of a near-by steam railroad. The rails near the structure and 
for a half mile or so on either side were supported out of contact 
with the soil on wooden ties, so that the potential measurement 
that was being taken was between the structure and a point sev¬ 
eral thousand feet distant. It seems almost needless to say that 
a potential measurement of this kind is worse than worthless as 
an indication of the electrical condition of the structure under 
examination. If we are to get an idea of the extent to which cur¬ 
rents may be flowing in a building by means of potential measure¬ 
ments, it is necessary that we take the potential readings between 
two points within or on the building itself and not between the 
building and some other structure more or less insulated from it. 
Similarly, if we wish to determine whether current is flowing into 
or out of a building, we should make the potential measurement 


123 


Electrolysis in Concrete 

between points on the building and thoroughly grounded points 
near by. Failure to keep these facts in view appears to have been 
responsible for a good many erroneous reports of damage to con¬ 
crete structures by stray currents. 

IV. PROTECTIVE MEASURES 

In the following discussion of means of reducing or preventing 
electrolysis troubles it is to be understood that the measures 
recommended are to be regarded as necessary only in those cases 
in which there is reasonable probability that the electrical condi¬ 
tions may become dangerous. In considering measures that may 
be taken to prevent damage or to cure electrolysis troubles it is 
not necessary to consider structures which have no metal imbedded 
in them, since, as pointed out above, these are immune from elec¬ 
trolysis effects. As regards reinforced-concrete buildings (or con¬ 
crete buildings with metal conduits imbedded in the concrete) 
there are two cases to consider—(i) new structures in process of 
building and (2) structures already completed. 

23. EXCLUSION OF SALT 

In the case of new structures of reinforced concrete salt should 
be omitted altogether if there is the slightest probability that they 
may ever be subjected to the action of electric currents. Calcium 
chloride is quite as bad as sodium chloride, it being the chlorine 
that does the harm. Since the addition of even a fraction of 1 
per cent of chlorine is sufficient to increase the rate of damage a 
hundredfold, it is impossible to use a sufficient quantity of salt to 
lower the freezing point of concrete perceptibly without making 
the structure decidedly more vulnerable to the action of electric 
currents. 

24. WATERPROOFING BELOW GRADE 

A good deal can be accomplished also by proper construction of 
the basement, foundations, and footings of the building. If 
beneath the foundations and outside the basement walls a layer 
of insulating material be placed, it will prevent the access of elec¬ 
tric currents through the building foundations. While such insu¬ 
lating materials can readily be made that will give permanent 


124 Technologic Papers of the Bureau of Standards 

increase of resistance, we have yet to see one that will, in the pres¬ 
ence of water, remain completely insulating over a period of years. 
We have tested a great many waterproofing membranes, but in 
the presence of water all have sooner or later begun to acquire 
considerable conductivity and show gradual deterioration. It is, 
of course, not necessary that such insulation should be perfect in 
order to be of value, since any considerable increase in the resist¬ 
ance which it may produce in the path of current flow will be useful. 
For this reason a waterproofing medium, such, for instance, as one 
made up of multiple layers of fabric treated with pitch, will have 
sufficient insulating value to be quite effective in preventing the 
passage of electric currents, and would probably be of considerable 
value even after the waterproofing has ceased to be perfect. 

25. ADDITION OF WATERPROOFING COMPOUNDS 

Attempts to increase the resistance of concrete by the addition 
of so-called waterproofing compounds to the cement before mixing 
have uniformly failed to give satisfactory results. As pointed 
out in the first section of this report, none of these compounds or 
mixtures that have been brought to our attention are of great 
value in this connection, and reliance should not be placed on 
them as a means of protecting structures against electrolysis. 

26 . CONSTRUCTION OF FOUNDATIONS 

A good deal can be done in the way of increasing the resistance 
between the building and ground by a proper selection of materials 
for the foundations. Blocks of granite, frequently used in such 
wx>rk, have a much higher resistance than concrete, a number of 
specimens tested by us showing, in the water-soaked condition, a 
resistance approximately one hundred times as great as that of 
wet concrete, and hence if granite blocks be interposed between 
the footings and the soil the tendency of the building to pick up 
stray currents will be greatly reduced. We regard this matter in 
most cases as of secondary importance if the potential differences 
in the region of the building are as small as usual, since any currents 
which a building may pick up in this way will be too small to do 
any appreciable harm. In some cases, however, the use of granite 
footings may be justified as a measure of precaution. 


125 


Electrolysis in Concrete 

The foregoing statements are not applicable to structures 
already built, but the following preventive measures may as a 
rule be applied to old as well as new structures. 

27. ELECTRIC WIRING 

In wiring a concrete building with direct-current circuits it is 
of the greatest importance that the construction be such as to 
preclude the possibility of either side of the circuit coming in con¬ 
tact with the concrete. The insulation should be of the best 
grade and the wires should be inclosed in continuous metal con¬ 
duit. When practicable periodic tests should be made on the 
insulation and any defect remedied. This can usually be done 
in the case of large structures, but in small structures generally 
it can not be considered practicable. If the power supply is a 
private plant belonging to the building the installation of ground 
detectors is desirable. If these precautions are taken it will not 
be necessary to insulate the conduits from the building as has been 
sometimes proposed. 

28. INSULATION OF PIPE AND CABLES 

By far the most important path of entry of electric currents 
into concrete structures from outside sources is through the pipes 
and lead cable sheaths which enter the building, and it is only 
through these paths, as a rule, that sufficiently high potential 
differences can be produced to result in damage to the structure. 
The most effective remedy, therefore, and at the same time a 
comparatively simple one, is to introduce insulating joints into 
the pipes before they enter the building. Such joints can easily 
be made, and are in fact now used in many places, although not 
so far as we are aware in this particular connection. The only 
condition to guard against is the possibility of developing too high 
a difference of potential across the joint which might give rise to 
electrolytic injury to the pipes; but this can be obviated by proper 
construction of the joint, as by giving it a long leakage path and 
by putting several insulating joints in series. 

When a pipe line passes through a building it will be necessary, 
if insulating joints are used at all, to use them on both sides of the 


126 Technologic Papers of the Bureau of Standards 

building. To use them on one side only would result in making 
the building more strongly positive or negative to the earth than 
it would be without such joints and thus the danger would be 
increased. If the insulating joints are put on both sides, however, 
there will be no likelihood of currents entering the structure to 
any apppreciable extent, except in special cases where the difference 
of potential between the broken sections of pipe becomes very 
high, say of the order of io or 15 volts or more. When this condi¬ 
tion occurs, however, it can be alleviated by shunting around the 
insulated section of pipe within the building by means of a copper 
cable, preferably an insulated one. 

It was stated above that lead-covered cables also form a possible 
source of entry of stray currents into buildings. It is, of course, 
possible to break up the continuity of lead cable sheaths by 
inserting insulating joints, but there are more serious objections 
to doing this than in the case of water or gas pipes. Nevertheless 
in some instances this is to be recommended; but it would be 
usually better simply to insulate the cable from the building, since 
only a very low degree of insulation would be necessary, such as 
would be obtained by carrying the cable on wooden supports and 
keeping it out of actual contact with the concrete and reinforcing 
material. 

29. MAKING THE REINFORCING MATERIAL NEGATIVE 

A method of protecting reinforced concrete structures that has 
frequently been proposed, viz, by making the reinforcing material 
continuous throughout the building and connecting it to the 
negative terminal of a low-voltage generator, should be referred 
to here, but only to point out the danger attending it. While 
there is no question but that corrosion of the reinforcing material 
might be prevented in this way, the experiments described in the 
first section of this paper show that under ordinary low voltages 
there is greater danger in having the iron negative than positive 
on account of the destruction of the bond in the former case. 
Any condition, therefore, which may cause the reinforcing material 
to become negative to the concrete should be carefully avoided. 


Electrolysis in Concrete 127 

30. IMPROVING THE NEGATIVE RETURN OF RAILWAYS 

In discussing means of preventing damage to buildings due to 
stray currents, we should not lose sight of the fact that, after all, 
the most effective way of reducing damage due to stray currents 
is by removing, as far as practicable, the cause of such currents. 
This means a proper design, construction and maintenance of the 
railway distribution system, whereby potential gradients in the 
earth are not permitted to reach such high values as to give rise 
to serious trouble. The protective measures against stray cur¬ 
rents mentioned above are rather to be regarded as precautionary 
ones, rendered necessary only on the failure of the railway com¬ 
panies to provide adequate means for returning their currents to 
their source. If the negative return systems of the electric rail¬ 
ways of this country were uniformly as good as those maintained 
in the principal countries abroad, the problem of damage to build¬ 
ings by stray currents would practically disappear. 

31. GROUNDING OF METALLIC CONDUITS 

The practice at present followed in many instances, and made 
compulsory in some city ordinances, of grounding all metallic 
conduits in contact with the concrete, is not to be recommended 
as a general rule. There are, of course, many cases under which 
such grounding would not bring about a condition dangerous to 
the concrete, but in some cases at least the results of such ground¬ 
ing might be serious. 

The above recommendation against the grounding of conduits 
is based on several considerations. If the ground were made on 
water pipes without insulating joints to prevent flow of current 
between the pipe system and the building as is commonly done, 
and if the district were one in which the pipes were at a higher or 
lower potential than the earth, the conduits would be made 
either anode or cathode, a condition which in general should be 
regarded as unsafe, and this condition would in fact be worse than 
the unrestricted entry of pipe systems into the buildings, which 
should be guarded against as pointed out above. 

69133°—14-9 


128 Technologic Papers of the Bureau of Standards 

If, on the other hand, the ground is made through a ground 
plate under or near the building this would bring all of the con¬ 
duit system to the same potential as the ground plate, and this 
being of small area compared to that covered by the building 
the footings of the building remote from the ground plate may show 
a considerable difference of potential against the ground plate 
and consequently against the conduit of the building, thus giv¬ 
ing rise to flow of current between the conduit and the structure 
itself. That this may be the case is quite evident from the fact 
that voltage surveys made in several cities in the course of 
this investigation show that in a great many instances large 
potential differences are found between two points in the earth 
that might easily fall within the space covered by a large build¬ 
ing. This is particularly true if the measurements are taken over 
distances at right angles to the electric railway tracks and very 
close thereto, in either the positive or negative areas. Places 
were found quite frequently where a difference of potential of 
several volts would be noted between points not over ioo feet 
apart. If a building were placed in such a locality, the different 
footings and different parts of the foundation would be at a con¬ 
siderable difference of potential with respect to each other and 
this would give rise to a tendency for the current to flow in at 
some of the footings and out at others. The resistance opposing 
this current flow would be mainly that of the footings themselves 
and the earth immediately beneath and such resistance would 
be encountered at both the entrance and exit of the current. If, 
however, ground plates be placed under the building at one 
locality and connected to the metal structure of the building the 
resistance in the current path would be reduced and larger cur¬ 
rents would flow through the building, producing either anode or 
cathode effects in the footings remote from the ground plate, 
according to the direction of current flow. While such voltages 
as would be likely to occur here would probably not give rise to 
any considerable trouble from anode effects, the cathode effects 
might be serious not only here but elsewhere in the building. 
The point to be emphasized is that a ground at one point does 
not assure relief from differences of potential, because of possible 


129 


Electrolysis in Concrete 

high local potential gradients in the earth. Of course, if the 
vertical walls and columns of the building were of nonreinforced 
concrete, and fairly dry, then the resistance would no doubt be 
sufficient to guard against trouble from this cause, but with any 
considerable amount of iron in the walls, either as reinforcement, 
piping, etc., such would not be the case and a local ground would 
have a tendency to increase the danger from this source. A 
ground covering the entire basement of the building, or a separate 
plate under each footing and under the foundation walls, all 
interconnected, would of course relieve this danger, but the 
desirability of attempting such extensive grounding is question¬ 
able, partly because of the cost and the lack of permanence of 
such grounds and their connection, and partly because grounding 
of this character would tend to increase danger from other sources, 
as described below. 

Another argument sometimes advanced in favor of grounding 
the metal work of a building, including the electrical conduits, to 
a ground plate, is that in case one of the power wires comes in 
contact with the conduit the grounding of the conduit would pre¬ 
vent any difference of potential between the building and the 
earth. An extensive study of electrical grounds in general, which 
was made incidental to this work shows that such is not the case. 
In the first place, it is practically impossible to make a ground 
through a metal plate that will have a sufficiently low resistance 
to prevent such differences of potential from arising due to a con¬ 
tact between wires and conduit. Tests conducted on grounds 
made at the Bureau of Standards, and also of those commercially 
used on low voltage secondaries and other places, show that these 
grounds are invariably of comparatively high resistance. The 
best grounds tested have been those made at the bureau and the 
results of these tests are instructive. These were made with 
plates 8 feet by 12 feet laid in wet ground with a bed of crushed 
coke below the plates and a layer of the same above, the whole 
being heavily salted and thoroughly flooded. In wet weather, 
when the ground is everywhere saturated with water, the resist¬ 
ance of these grounds is about 15 ohms, as shown by measure- 


130 Technologic Papers of the Bureau of Standards 

ments against each other and against the water-pipe system of the 
city of Washington. During a dry period the resistance is much 
higher. Consider, now, that the metal work of a building, includ¬ 
ing the electrical conduit, is connected to such a ground and that 
the wires become grounded on the conduit. The current can go 
to ground both by way of the ground plates and also through the 
footings and foundations, the two paths being in parallel and inde¬ 
pendent of each other. If the circuit be 110 volts, several amperes 
may flow through the ground plate, but this, under usual condi¬ 
tions, would not cause any disturbance in the system and would 
probably go unnoticed except in a very small building using but 
little power. This parallel circuit through the ground plate would 
have no more effect on the potential of other parts of the building 
than the throwing of a load of several amperes in parallel with a 
lamp on an ordinary lighting circuit would have on the potential 
of the lamp. It would not, therefore, have any tendency to pro¬ 
tect the structure from damage due to contact between a power 
wire and its conduit. On the other hand, it is extremely difficult 
to insure that all parts of the conduit shall be at all times in perfect 
electrical connection with the other metal parts of the building, 
because considerable resistance may be developed at joints, so 
that the portion of the conduit in contact with the wire may be 
but imperfectly connected to the ground plate. If at the same 
time the reinforcing material be connected to a ground plate there 
would be a great tendency for current to flow from conduit to 
reinforcing material or the reverse. Owing to the close proximity 
of conduit and reinforcement in many places, a comparatively 
low resistance joint sufficient to take up 2 or 3 per cent only of 
the voltage of the line (which would require but a fraction of an 
ohm in the case being considered, viz, a 15-ohm resistance in the 
ground plate) would give rise to a potential difference of several 
volts between conduit and reinforcement, which might do great 
harm, especially if the reinforcement is cathode. 

While, of course, it would be possible, by going to considerable 
expense to make a ground of lower resistance than those just con¬ 
sidered, it does not seem that it would be practicable to make and 


Electrolysis in Concrete 131 

maintain permanently a sufficiently low resistance to give the 
protection sought. 

It is desirable, however, to connect the metal work of the build¬ 
ing together as far as practicable, provided such metal work is not 
in turn connected directly to pipe lines and cables entering the 
building. In other words, it is recommended that conduits, and 
such pipes as are separated from their mains by means of insu¬ 
lating joints, be interconnected electrically, but that this group of 
interconnected metal work should not be -grounded directly to 
earth for the reasons given above. In addition, it may be said 
that if the low-voltage side of alternating-current circuits be 
grounded at the neutral point there is no material advantage to be 
gained by grounding the conduit. 

V. CONCLUSIONS 

The following conclusions are drawn from the investigations: 

1. The observations of previous investigators that the passage 
of current from an iron anode into normal wet concrete caused 
the destruction of the test specimen by cracking the concrete were 
only partly confirmed. This effect was found not to occur in 
most of the specimens tested when the potential gradient was less 
than about 15 volts through a distance of 3 inches, or about 60 
volts per foot. These figures must be considered as but roughly 
approximate as they depend much on conditions. 

2. Of the numerous theories that have been advanced for the 
cracking of reinforced concrete due to electric current that one 
which attributes it to oxidation of the iron anode following elec¬ 
trolytic corrosion has been fully established. The oxides formed 
occupy 2.2 times as great a volume as the original iron, and the 
pressure resulting from this increase of volume causes the block 
to crack open. 

3. Metals which do not form insoluble end products of corrosion 
and all noncorrodable anodes never cause cracking of the concrete 
as a result of the passage of an electric current. 

4. The mechanical pressure developed at the iron anode surface 
by corrosion of the iron has been measured in a number of cases 


132 Technologic Papers of the Bureau of Standards 

and has been found to reach values as high as 4700 pounds per 
square inch, a value more than sufficient to account for the 
phenomena of cracking that have been observed. 

5. Suggestions of some engineers 31 that copper-clad steel or 
aluminum be used as reinforcing material have been shown to be 
impracticable, since the copper coating is readily destroyed and 
the aluminum is attacked by the alkali in the concrete. 

6. Corrosion of iron anodes even in wet concrete is very slight 
at temperatures below about 45 °C (ii3°F). 

7. For any fixed temperature the amount of corrosion for a given 
number of ampere-hours is independent of the current strength. 

8. The lack of corrosion of the iron at temperatures below 45 0 C 
is due to the inhibiting effect of the Ca(OH) 2 and possibly other 
alkalies in the concrete. 

9. The rapid destruction of anode specimens of moist concrete at 
high voltages (60 to 100 volts or more) is made possible mainly 
by the heating effect of the current, which raises the temperature 
above the limit mentioned above. If the specimen be artificially 
cooled no appreciable corrosion occurs, and no cracking results. 

10. The potential gradient necessary to produce a temperature 
rise to 45 0 C with consequent corrosion, in the specimens used, 
was about 60 volts per foot. For air-dried concrete it is much 
higher. This shows that under actual conditions corrosion from 
stray currents may be expected only under special or extreme 
conditions as noted below. These figures are but roughly approxi¬ 
mate since they will vary greatly with the conditions, such as the 
size, form, and composition of the specimen, but they serve to show 
the order of magnitude of the voltage required to produce trouble. 

11. Since the passivity of iron in concrete is due chiefly to the 
Ca(OH) 2 present it appears probable that old structures in which 
the Ca(OH) 2 has been largely converted into carbonate will be 
more susceptible to the effects of electric currents than com¬ 
paratively new concrete with which the foregoing experiments have 
been made. The increase in the efficiency of corrosion would, 
however, be at least partly offset by the increase in the resistance 
of the concrete which would accompany the change. 


Magnusson and Smith: The Electrolysis of Steel in Concrete, Proc. A. I. E. E., 30, p. 939 . 



133 


Electrolysis in Concrete 

12. The addition of a small amount of salt (a fraction of i per 
cent) to concrete (as is frequently done to prevent freezing while 
setting) has a twofold effect, viz, it greatly increases the initial 
conductivity of the wet concrete, thus allowing more current to 
flow, and it also destroys the passive condition of the iron at 
ordinary temperatures, thus multiplying by many hundreds of 
times the rate of corrosion and consequent tendency of the con¬ 
crete to crack. Salt should, therefore, never be used in structures 
that may be subjected to electrolytic action, Further, reinforced 
concrete structures built in contact with sea water, or in salt 
marshes, are more susceptible to electrolysis troubles than con¬ 
crete not subjected to such influences. 

13. Specimens of normal wet concrete carrying currents increase 
their resistance a hundredfold or more in the course of a few 
weeks, which fact still further lessens danger of trouble. 

14. The rise of electrical resistance is probably due to a number 
of causes among which are the precipitation of CaC0 3 within the 
pores of the concrete thus plugging them up. A slight amount 
of salt tends to prevent this precipitation and interferes with the 
rise of resistance, thus still further emphasizing the detrimental 
effect of salt. 

15. Contrary to the observations of previous investigators 
there was a distinct softening of the concrete near the cathode. 
This begins at the cathode surface and slowly spreads outward, 
in some cases as far as one-fourth inch or more. After exposure 
to the air this softened layer becomes very hard again, but 
remains brittle and friable. 

16. The softening effect at the cathode noted above, caused 
under the conditions of the experiments, practically complete 
destruction of the bond between reinforcing material and the 
concrete, reducing it to a few per cent of its normal value. 

17. Unlike the anode effect which becomes serious in normal 
concrete only on comparatively high voltages, the cathode effect 
develops at all voltages used in the experiments, the rate being 
roughly proportional to the voltage in a given specimen. 

18. In general the cathode effect occurs under conditions 
which may not infrequently occur in practice and is therefore 


134 T echnologic Papers of the Bureau of Standards 

probably a more serious matter practically than the anode effect 
about which so much has been written. This trouble is unlikely 
to be serious, however, except where the concrete is wet and the 
potential differences rather large. 

19. The softening of the concrete at the cathode is due chiefly 
to the gradual concentration of Na and K near the cathode by 
the passage of electric current. In time the alkali becomes so 
strong as to attack the cement. 

20. Softening at the cathode is increased by increasing the Na 
and K content of the cement, and reduced by diminishing this 
content, at least within the range below 10 per cent of the total 
salts. 

21. The softening of the concrete has never been observed, 
except very close to the cathode, the main body of the concrete 
remaining perfectly sound. Numerous tests show conclusively 
that the crushing strength of the main body of the concrete is not 
reduced even when the potential gradient is maintained at 175 
volts per foot for over a year. 

22. Because of the cathode effect noted above, the proposal to 
protect reinforced concrete buildings by maintaining the reinforc¬ 
ing material cathode as by a battery or booster would be much 
more dangerous than no protection at all. 

23. Aside from slight heating, which is usually negligible, the 
only effect which an electric current has on unreinforced concrete 
is to cause a migration of the water soluble elements. Conse¬ 
quently, in the absence of electrodes, the ultimate effect of current 
flow on the physical properties of the concrete is not materially 
different from that of slow seepage, which also removes the water 
soluble elements. Nonreinforced concrete buildings are there¬ 
fore immune from trouble due to stray earth currents. They 
might, however, be injured by the grounding of power wires 
within the structure since these or the inclosing conduits would 
then act as electrodes. 

24. Conditions arise in practice which give rise to damage due 
to stray currents, but the danger from this source has been 
greatly overestimated. While precautions are necessary under 
certain conditions, there is no cause for serious alarm. 


135 


Electrolysis in Concrete 

25. If reinforced concrete could be thoroughly waterproofed, it 
would greatly increase its resistance and diminish accordingly the 
danger from either the anode or cathode effects. It should be 
emphasized, however, that waterproofing to prevent electrolysis 
is a much more difficult matter than waterproofing to maintain a 
moderate degree of dryness, because of the much higher degree of 
waterproofing required in the former case. It has been found 
that practically all of the waterproofing agents now on the market 
that are intended to be mixed with the concrete, are of little value 
as preventives of electrolysis. Waterproofing membranes, etc., 
applied to the surface can be made more effective and when prop¬ 
erly applied may have considerable effect in preventing the entry 
of earth currents into the concrete. 

26. Painting or otherwise coating iron with an alkali resisting 
metal preservative before embedding it in concrete may serve to 
minimize the dangers of electrolysis, but no such coating has been 
found that does not prevent the proper formation of the bond 
between the concrete and iron when the concrete sets. 

27. In order to insure safety of reinforced concrete from elec¬ 
trolysis the investigation shows that potential gradients must be 
kept much lower in structures exposed to the action of salt waters, 
pickling baths, and all solutions which tend to destroy the passive 
state of iron. 

28. All direct current electric power circuits within the concrete 
building should be kept free from grounds. If the power supply 
comes from a central station the local circuits should be periodically 
disconnected and tested for grounds and incipient defects in the 
insulation. In the case of isolated plants ground detectors should 
be installed and the system kept free from grounds at all times. 

29. All pipe lines entering concrete buildings should, if possible, 
be provided with insulating joints outside the building. If a 
pipe line passes through a building and continues beyond, one or 
more insulating joints should be placed on each side of the build¬ 
ing. If the potential drop around the isolated section is large, 
say, 8 or 10 volts or more, the isolated portion should be shunted 
by means of a copper cable. 


136 Technologic Papers of the Bureau of Standards 

30. Tead-covered cables entering such buildings should be isolated 
from the concrete. Wooden or other nonmetallic supports which 
prevent actual contact between the cable and the concrete will 
give sufficient isolation for this purpose. Such isolation of the 
lead-covered cable is desirable for the protection of the cable as 
well as the building. 

31. The interconnection of all metal work within a building is 
an advantage where practicable, provided that all pipe lines enter¬ 
ing the building are equipped with insulating joints and lead cables 
are taken care of as indicated in the preceding paragraph, but the 
grounding of such interconnected metal work or any part of it to 
ground plates or to pipe lines outside of the insulating joints is to 
be strictly avoided. 

32. In making a diagnosis of the cause of damage in any particu¬ 
lar case, the fact that a fairly large voltage reading may be obtained 
somewhere about the structure should not be taken as sufficient 
evidence that the trouble is due to electrolysis. The distance 
between the points, and particularly the character of the inter¬ 
vening medium, are of much greater importance than the mere 
magnitude of the voltage reading. As a precautionary measure, 
however,, all potential readings about a reinforced concrete struc¬ 
ture should be kept as low as practicable. 

Washington, March 19, 1913. 


APPENDIX.—BIBLIOGRAPHY OF ELECTROLYSIS IN 

CONCRETE 


Max. Toch, The Electrolytic Corrosion of Structural Steel, Jour. Am. Electro-Chem. 
Soc., 9 , p. 77; 1906. 

A. A. Knudson, Electrolytic Corrosion of Iron and Steel in Concrete, Trans. A. I. 
E. E., 26 , p. 231; 1907. 

L. P. Crim, Electrolytic Corrosion of Iron, Thesis, University of Washington, 1908. 

A. J. Nicholas, Tests on Effect of Electrolysis in Concrete, Eng. News, 60 , p. 710. 

A. S. Langsdorf, Electrolysis of Reinforced Concrete, Jour. Assn, of Eng. Soc., 42 , 

p. 69; 1909. 

Max. Toch, Paint, Concrete, and Corrosion, The Iron Trade Review, 46 , p. 1007; 1910. 
O. L. Eltinge, Tests on Effect of Electrolysis in Concrete, Eng. News, 63 , p. 372. 

G. B. Shaffer, Corrosion of Iron Embedded in Concrete, Eng. Record, 62 , p. 132. 
Nicholas, Further Tests on the Effect of Electric Current Upon Concrete and Steel, 

Eng. News, 64 , p. 590. 

Abstract of paper by C. F. Burgess, Electrolytic Corrosion of Iron in Concrete, Eng. 
Record, 63 , p. 272; 1911. 

Magnusson and Smith, The Electrolysis of Steel in Concrete, Proc. A. I. E. E-, 30 , 
P- 939- 

Barker and Upson, Experimental Studies of the Electrolytic Destruction of Rein¬ 
forced Concrete, Eng. News, 66, p. 10. 

Seven-hundred-word letter from B. C. Worth followed by a 1400-word reply from H. P. 
Brown, Prevention of the Electrolytic Destruction of Reinforced Concrete, Eng. 
News, 66, p. 152. 

H. P. Brown on Allentown case, Serious Injury to a Reinforced Concrete Building 
by Electrolysis, Eng. News, 65 , p. 684. (See also Eng. Record, V. 64, pp. 33 and 
144.) 

Brief abstract of a report by a German commission on the Electrical Resistance of 
Concrete, Eng. News, 65 , p. 696. 

A. S. Cushman, Conservation of Iron, Jour. Franklin Inst., April, 1911, and Eng. News, 
65 , p. 523. 

C. M. Chapman, The Effect of Electrolysis on Metal Embedded in Concrete, Proc. 
Natn. Assn, of Cement Users, 7 . 

A British Example of Electrolytic Corrosion of Steel in a Reinforced Concrete Struc¬ 
ture, Eng. News, 66, p. 207. 

M. Toch, The Condition of the Steel in Gillender Building, Eng. News, 66, p. 204. 
Hayden, Electrolytic Corrosion of Iron by Direct Current, Jour. Franklin Institute, 

172 , p. 295. 

Heyn and Bauer, Mitteillungen K’gl’n Materialprufungsamt, 1908, p. 45. 

H. P. Brown, Electrolysis of Reinforced Concrete, Eng. News, 68, p. 150; 1912. 

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